To do/ not to do

What moments in your 20's define you 20's?
Will we only know when we are 40? Older people always says that phrase that they wish they were 25 again, and it worries me because i wonder what is it! What am i not realizing or, am i doing those things that those 40 year olds regret not having done or wish they were doing again. I guess the only way to avoid that is to do anything you want and not to limit yourself in anyway. Are the 40's defined by wishing you were 20? lol i sure hope not, and i doubt that it is. : )
So in light of this i googled... things about being in your 20's, i found both the things you have to do and those youll regret when your 40.

To do:
Surround yourself with wise mentors
Become a lifelong learner
Travel
Learn to listen and handle criticism well
Develop an active, healthy lifestyle
Read a classic
Go on an overseas missions trip (ugh)
Create a monthly budget
Start a Roth IRA (RRSP)
Buy a used car
Understand basic investment principles
Go to a concert
Learn a foreign language
Start a blog
Get your college degree
Pay off credit cards
Stay in a hotel that costs over $200 a night
Read the Bible cover to cover (not going to happen)
Explore your family of origin issues (positive and negative) and pursue growth
Figure out the type of person you want to marry
( http://www.schaefersblog.com/20-things-to-do-in-your-20s/ )
Not to do
10. Body Piercing Plugs
9. Risque Internet Pics
8. Tattoos
7. Choosing Your Best Friend’s Girlfriend Over Your Best Friend
6. Getting Married Too Young
5. Not Traveling (Enough)
4. Not Finishing School
3. Smoking
2. Bad Credit
1. Not Spending More Time With Your Parents
( http://coedmagazine.com/2009/11/27/10-things-from-your-twenties-youll-regret-when-youre-forty/ )

Good to see some things overlap such as travel, credit, ... lol