Obviously, nobody thinks about the choice because the choice isn't made to matter very much, except in the extreme long-term of avoiding the aging penalties you receive at 50. For this reason, there's no mechanical sense in choosing any age other than the minimum the GM lets you get away with. But I don't think it's worth figuring out some sort of life events table that scales with your age and you have to make an excel spreadsheet just to calculate.
So, money. How about one extra copper at character generation for each of your first twenty years? And, one silver piece for each year after, till you're 50, then you get 1 GP per year. Age becomes a little bit of a Faustian bargain - more immediate power right now, during character generation, in return for bringing dementia and incontinence just a little bit closer.
Is it balanced? Using my 1:10:40 GP:SP:CP standard, a 55 year old character would effectively get 85+3d6x10 silvers at character generation. Probably not enough to balance out the chance of losing five points of attributes. But maybe enough to merit some thought about it.