If only I knew then, what I know now. If I had a dollar for every time I've heard an adult say this, I could have paid off my student loans by now. For everyone entering their 20s, here are 21 things people wish they knew by your age.

1. Say yes more often.

Bite the bullet and put your big girl panties on, because life's not meant for the boring, sweetheart. Go out on a Tuesday. Cut your hair short and dye it blonde. Go on the date with the nerdy guy crushing on you. Take that road trip. Whatever it is you've been afraid to do, just start saying yes!

2. Don't be afraid to say no more often.

On another note, stop being afraid to say no to people. FOMO is very real, but so is that C you're getting in American History and that hangover you've had for three days straight.

3. Travel, travel, travel.

Spring break in Mexico? A semester in Prague? A weekend of binge drinking and bad decisions at a lake house in Wisconsin? It doesn't have to be huge, but you learn the most about yourself when you're experiencing new cultures. It's not like you'll be missing much at your college in the cornfields anyway.

4. People aren't against you; they are for themselves.

It's time to put your sixth grade skinny jeans and band tees away, because the world is not out to get you. When someone screws you over, and they will, know that they aren't rooting for you to fail. They are just rooting for themselves to succeed. So be ready to have your own back.

5. The bars can wait.

After you turn 21, you'll have every weekend to go to bars, and house parties will practically be a thing of the past. So go to that house party, make out with that boy in the hallway and put your fake ID to rest (I promise it doesn't look as real as you think, anyway).

6. Hangovers are very real.

Even though you swear you only had like three vodka cranberries, your bathroom floor will be your new best friend. So enjoy your $10 handle of vodka now, because in few years you won't dare to touch the stuff. Pro tip: Coconut water, and when that fails, another vodka cranberry.

7. Listen to your mother.

OK, so call me a hypocrite, but I learned this one the hard way. Moms have a secret sixth sense when it comes to people. So if the mothership doesn't like your new boyfriend or disapproves of your newfound best friend, dump them. Mom's right. He's a scrub, and she'll probably try to steal your next boyfriend.

8. Start caring about school work.

As boring as your History of East Asia class is, and trust me I know, suck it up and get that A. You'll be thankful when senior year rolls around and your heading to your top choice grad school, or don't, and maybe they'll be impressed that your GPA matches the breathalyzer you took last weekend.

9. Choose your battles.

For example, that guy in your poli-sci class who still thinks a woman shouldn't be president definitely deserves a piece of your mind. But that girl who called your house the "easy sorority" is not worth your energy — and she's probably right.

10. Take care of your skin.

Hopefully you do this already. But for those who don't, your 20s are the perfect age to start. Those years of tanning beds and nights of slept-in, inch-thick makeup will catch up with you, and it won't be pretty.

11. You need something to believe in.

It doesn't matter if it's a religion, science, a cause or the lyrics to your favorite song. But find something you know you believe in. It will guide you through the dark times and humble you during the good times.

12. It's OK to date around.

Date around, learn what you like, what you don't like, find out what you deserve and what you want in a relationship. Practice makes perfect right?

13. Appreciate everyone you meet.

No matter what role they played. Chances are they changed your life somehow or you changed theirs. Yes, even the friend whose knife is still in your back. You don't have to appreciate what they put you through, but you will thank them one day for how it made you better.

14. When you meet people, forget what you know about them.

Seriously. Forget everything. Meet someone with a completely open mind. You have no idea what their story is or who they really are. Give them a clean slate, and you may be surprised with what you learn. Also, be kind to everyone you meet. You never know how hard it was for them to get out of bed that day.

15. Try to make friends who are different than you.

Different ages, different religions, different sexual orientation, everything. Don't box yourself in by setting boundaries on friendship. Some of your best friends will be from completely different walks of life.

16. Find something you're good at and master it.

Everyone has a gift. Find yours and then share it with the world. Someone out there wishes they could do what comes naturally to you.

17. Do absolutely nothing and enjoy it.

Stay home and binge watch Netflix or float in your pool for four hours and enjoy the sun. Take the time to do absolutely nothing and enjoy it. You might not get the chance again until retirement. Seriously.

18. Stop making excuses.

When you're young you have the most time, the most energy, the best health and the fewest responsibilities. The world is literally at your feet. So stop making excuses and start checking off your bucket list. It only gets more complex from here.

19. It's OK to not have it all figured out.

When 21 comes around, it'll feel like the rest of your life came with it. Suddenly everyone around you will seem to already have job offers, be in a serious relationship or just seem more confident in their path than you are. A little secret? No one has it all figured out; some people are just better at pretending.

20. Save your money.

I seriously can't stress this enough. I know all college kids are broke, but do you really need that third pair of Hunter boots or B-dubbs every Thursday night? The older you get the more you wish you'd use that money on experiences instead of things. Or dare I say it, your student loans?

21. Cherish your family.

OK, so maybe they are a little embarrassing at times. And you probably don't see eye to eye on everything. But hear me out when I say the older you get, the more you'll realize all that your family does for you. Your siblings will become your best friends, and you'll wish you had the years spent fighting back. As for your parents, stop telling them to get out of your room and start telling them thank you and I love you. Whether they are family by blood or by roots, cherish them.

Bonus 22. Learn how to do things for yourself.

Learn how to do your taxes, how to buy a car, how to cook something other than mac and cheese. Make your own appointments, start paying your own bills (even if it's just your monthly tanning at first). Know how to change a tire, jump a car, get around the city. Whatever it is, start learning as much as you can as early as you can. You'll be thankful later.

**CD: Thank you Megan Prejzner and Anna Newman for helping compose this list with perspectives from different age groups!