Man, this is complete nonsense. You should not feel old at 20. You haven't experienced anything. I remember when people would tell me that being a teen was the time of your life. If being broke, living at home, not having a car and not getting ass was the time of my life, then life would suck. Then it was college and it got better. But the time of your life is when you leave your parents house. You can do what you want, when you want. Bring girls over at anytime. Nothing kills a sexy intimate evening like bringing a girl back to the bed you've had since you were 5 yrs old with your parents in the other room. For most people, life starts after college. Living is a dorm doesn't count. I mean when you have a career, not a summer job. When cash is rolling in. That my friends is when you start living. I'm 26, i'll be 27 next month. I don't feel old, I feel great. I'll be going to grad school soon and i'm looking forward to advancing myself. If you are feeling old just 2 years out of high school, then something is wrong with your life. Dude, you can't even get into a casino or a bar. Your life has not even begun my friend. You have not experienced much.
Also, look at it this way. Men appreciate with time, yet women depreciate with time (Monica Belluci aside). It's natures cruel joke. Most of hollywoods leading men and sex symbols are in their 40's, 50's and even 60's. Brad Pitt, Tom Cruise, Denzel Washington, Pierce Brosnan. Hell, women still want to f*ck Sean Connery, grey haired, sagging teats and all.
