Using the advanced search bit of livejournal (if you have a paid account) you can actually find out who on your friends list is what age – that is, of those who have dared to disclose. You have to be a little cautious with it because a) the cut-off age is birthdays, so “between 21 and 26” actually means people whose ages run from 21 to 25, and b) the search database isn’t totally up to date, so a few of the most recent additions to my friends list don’t show up. Having made those corrections:

Of 68 “mutual friends”, 46 (68%) have given their ages in their lj info.
33 of those 46 (72%) are younger than me
3 (including me) are my age – 37
10 (22%) are older than me

Taking it in five year cohorts, there’s an interesting effect – a bulge at the lower end, reflecting the general age profile of livejournal, and another bulge around my own age, reflecting I suppose people who I have most in common with in terms of life experience:

I just thought you’d like to know.