Getting older is tough: you struggle to keep up with fads and fashion as life seems to get faster by the minute. But one of the strangest things about growing up is finding out how many things you believed when you were younger are completely false. Here are 16 "facts" you might still believe:

1. 1 human year is 7 dog years

We've tackled this popular pet myth before, but it has incredible sticking power. If you dog is four years old, that means it's really 28 in dog years, right? Probably not. For one thing, the hundreds of different breeds of dogs don't age at the same speed, and have very different life expectancies.

As a rule, bigger dogs age much faster than smaller ones, but there are little dogs (like Beagles) that tend to lead short lives. It's best to do a little research on your dog's breed to work out how old they "really" are.

2. Cracking your knuckles causes arthritis

Everyone has heard that popping your knuckles (or your other joints) will give you arthritis, and this is the kind of old wive's tale that sounds like it could be true. But studies have shown that popping or cracking your knuckles does not cause osteoarthritis.

Doctor Donald Unger took the research a step further, since some people still weren't convinced. For more than 60 years, he cracked the knuckles on his left hand but not his right. Neither of his hands developed arthritis or any other chronic conditions. The "pop" you hear is a type of cushioning liquid called synovial fluid moving in your joints.

3. Bulls hate the color red

Of course we all believe this: we grew up watching cartoons where bulls would chase anything painted red. And it is true that matadors wave a red flag at the animals during a bullfight. So why wouldn't this be true?

Well for one thing, bulls are color-blind to the color red. It's not the color of the cape - or muleta - that the matador waves at the bull that makes him charge. The animal has been riled up, stabbed with pointy sticks and pushed into an arena. If someone waved a cape at you after all that, wouldn't you be a little ticked off?

4. Twinkies last forever

The old joke says that the only two things that will survive a nuclear war are Twinkies and cockroaches. For some reason, people got the idea in their heads that the chemicals in these addictive snacks will keep them fresh for hundreds of years.

But as a Hostess executive told The New York Times in 2000, Twinkies are "on the shelf no more than 7 to 10 days." With modern preservatives, the snack cakes are safe to eat for about 45 days, but after that you're pushing it.

5. Jesus was born on Christmas Day

All of our favorite Christmas movies and TV specials mention that Jesus was born on Christmas Day, but that never actually comes up in the Bible. Scholars say clues in the holy text actually point to September as his likely birth date.

So why do we celebrate his birth in December? In the year 350 Pope Julius I chose the date, making it the official day to celebrate the birth of Jesus. Experts say December 25th was probably picked to line up with older Pagan holidays marking the Solstice.

6. People used to think the Earth was flat

It can be nice to look back at the past and think about how much smarter we all are today. It's a shame that's not true in this case. Since ancient Greece, people have known that the earth is round (roughly). Ancient scientists even made a pretty accurate calendar by measuring shadows in different cities.

All of the supposed confusion about the Earth being flat is a modern invention. It has even wormed its way into other historical stories, like Christopher Columbus's famous voyage. The explorer was trying to sail to India, not the end of the Earth.

7.  Families had their names changed at Ellis Island

Many people claim that their families had their name changed to sound "more American" by officials at the Ellis Island immigration inspection station. For example, a name like Tamio might become Tommy, or Finkelstein to Finkel. Maybe your family has their own story about a historical name change.

But nobody's name was actually "changed" at Ellis Island. Workers there just logged the names on the shipping manifests from their home countries. The fact is that immigrants have lots of reasons to change their names, like to make them simpler, easier to pronounce, or so they're easier to write in English.

Until recently, changing your name was as easy as picking a new name and using it, which is what many families did.

This next one is pretty surprising...

8. Sharks don't get cancer

Sadly, they do. While it's "common knowledge" that these ocean predators have a natural immunity to the disease, scientists have actually spotted many cancer cells in shark bodies. Recently, they've even found sharks with tumors in very rare cases.

It seems the popular idea that sharks don't get cancer came from I. William Lane, author of the book Sharks Don't Get Cancer. Lane also sold shark cartilage as a natural cancer cure.

9. Coffee is made from beans

How could this be wrong? Every coffee commercial mentions fresh roasted beans, the specific kind of beans, and the way the beans are blended. While that's true, the coffee "bean" isn't what it seems. These are really pits from small fruit.

Coffee trees grow small berries that are similar to cherries. The pit inside these fruits is called the coffee bean, and that's what we roast to make our favorite beverage. Does that mean my daily cup of joe counts as a serving of fruit?

10. JFK once told a crowd "I am a jelly donut"

History teachers love a good story that can get their class to pay attention for a minute or two, and that's just what this is - a good story. During a speech in West Berlin in 1963, Kennedy proudly said "Ich bin ein Berliner," which supposedly translated to "I am a jelly donut" instead of "I am a Berliner."

While Germans do enjoy a kind of jelly donut called the Berliner Pfannkuchen, they knew that the president wasn't referring to that during his speech. If you want to call yourself a jelly donut, you would say "Ich bin ein Pfannkuchen."

11. Different parts of your mouth taste different flavors

In 1901 a German psychologist named Edwin Boring drew up a map of the human tongue with different "zones" to taste each of the four flavors: bitter, sour, salty and sweet. Despite the fact that Boring had no proof to back up his system, his map found its way into biology textbooks for decades.

In fact, every part of your tongue can taste all of the different flavors described by Boring. There's even a fifth flavor called umami, for savory foods like ketchup.

12. George Washington had wooden teeth

If you can remember two facts about this Founding Father from history class, one is probably that he became America's first president, and the second is that he had wooden teeth. But like the famous story of George chopping down a cherry tree as a boy, this isn't true at all.

In fact, Washington used multiple sets of dentures from a number of sources, but none of them were made of wood. Instead, they were made from human teeth, cow and horse teeth, hippo or elephant ivory, and even copper.

13. Kids can get a "sugar rush" from eating sweets

While there are lots of good reasons not to let your little ones eat candy and cake, there's no evidence that sugar will make them act out. Researchers studied the behavior of kids who had a high-sugar diet compared to kids who ate no sugar, and found no difference.

The fact is that kids act out all the time, and sugar just takes the blame. If children are rowdy at a birthday party, blame the fun atmosphere and not the cake.

14. "X-Mas" is a non-religious way to say Christmas

Every year there are stories of people getting angry about "Merry X-Mas" signs. Some people see this phrase as a way to mention Christmas while leaving Christ out, and a sign that our country is becoming less religious. But in fact the X in X-Mas stands for Christ.

The Greek word for Christ is Χριστός (Christos) and X became a short version of the name during the Middle Ages, as monks translated Greek texts. The first use of X-Mas to mean Christmas dates back to 1551.

15. Liquor "cooks out" of food

Adding a little red wine to a recipe adds some great flavor, and common knowledge tells us that the alcohol in the wine "bakes out" of the food over time. This is one of the older food myths of all, and amateur chefs should know it's not true.

After cooking for an hour, 25% of the alcohol in a dish is still there. Even after two hours as much as 10% of the alcohol remains. That's probably not enough to push you over the limit, but it's something to consider.

16. You have to wait 24 hours to file a missing persons report

We'll blame this one on all of the Law and Order that we've watched over the years. While many police departments will warn you to wait a little before reporting a friend or family member missing, it's obvious that this shouldn't be a rule. If there are signs of violence or other reasons to worry for a person's safety, police want to start looking for them right away.

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