I don't really care who is behind the avatar until I get to know them and then age still does not matter (most of the time)
SL is a fantasy world where you can be almost anything you want - so when you have the keys to the sweet shop why stick to marshmallows!
One thing I will say if you try to make yourself as good looking as possible then its difficult to stand out.
But I have found that those avatar do a little different that differs from the media norm of beautiful, successful people and go for older, fatter etc tend to be more interesting.
Something along the lines of - you can look perfect so why don't you ? - already some mystery to be solved.
Whereas the supermodels are all hair make style and often no substance.
I for one am 44 in RL but my avatar is a perfect 20-30 - what can I say ? Clearly I am not interesting and just think about hair and make up ..........