I don't really like the idea to be honest, and I'd imagine there'd be a lot of other people (ie. parents) who wouldn't be too crazy about it either. There's a very strong public opinion (mostly generated by the media) that internet chat networks are only full of teen sex talk and paedophiles. Something built into clients which, let's be honest here, has really no other use than for someone to quickly decide "is this person of the sex I'm attracted to and are they in the age range I like", would only further that reputation.
