Once I hit 20, none of my birthdays seemed very meaningful (nothing has really changed from 21-23, and I don't imagine it will really matter once I'm 24 either). I haven't really noticed any age-related declines yet, but I do feel like my development is levelling off quite a bit. So I do occasionally have to stop and think about how old I am.

I suspect looming mortality and a sense of urgency (career prospects, life milestones, etc), will make me increasingly aware of my age as I go from 25 and beyond.

A lot of people I work with are 29-34, and they're all stressing about age a bit. I think that '30' really hits you, because that's such an officially grown-up age (not that you're old or anything, you're just so far removed from being a kid). The single women at work in their 30's, are all getting a bit anxious, relationship-wise (not saying they should be, they just are). I have heard egg talk more than once in the last month.

One thing I am finding weird is thinking of 1999 as 15 years ago.