I don't remember if it was TC, or another author on another site, but I remember a quote about 30 being the new 20, 40 being the new 30, and so on. I think the author was making a point that, with longer lifespans and more job-hopping, more people aren't settling down as quickly.
I'm 29, will be 30 in about six months. I often remark to myself (sign of senility?) that I feel like I'm 24. I know I'm in better shape than when I was 24 (or 20, for that matter).