Well: I'll take the bait.
It really depends on my mood!
and, I'd say, time I have allocated (= budgeted) for the meeting.
OK, so how and why:
- well, for a half hour encounter, the age really is of a much lesser significance to me than for e.g. an hour session.
- for the shorter session, e.g. the ability of the lady to be a great conversationalist with me, is not as important as if we met for one hour (or more);
- certainly for the 1 hr+ sessions, I'd want a good conversationalist (as well as everything else that is important here): thus, generally a bit older helps.
Having said that: the conversations need not be about redesigning the world; but even what I might consider fun, is not necessarily what an 18-year old conisders fun.
So - what about the other end of your spectrum: 50ish.
I have a some great sessions in that age bracket (being older than that myself).
In general: I try to check out reviews for ladies having provided excellent experiences: age, nor size (for that matter!) being as important!