i'm 30 and feel/look as young as I did in high school. Have all my hair, have yet to get hair in unwanted places, weigh what i did sr yr of high school, faster than ever (compared to all american in college), have more money than ever, have a good job resume, have more free time than ever, am more independent than ever, & ultimately 1000 times happier than ever.
Not getting married has helped. While I don't spend much time watching tv (many of the old people I know have "their" shows), when I do it's usually MTV, ESPN, & E!. I can't think of much that is more annoying than my friends/family who don't know hit songs or how times change when it comes to dressing/grooming/etc. I don't spend an hour commuting in the car everyday to work. That's huge too. And finally, I run twice a day & have comparable running goals that I had in college. I expect the times to be the same or faster, the abs to be as strong, etc. Having the same goals as I did when I was younger (and the goals still being realistic) has made 28, 29, and 30 yrs old feel very similar to 20, 21, and 22 yrs old. No reason to have a plateau at 30 or earlier when Lagat is out there doing his thing at his age.
that's my opinion.