if you're wanting to model for the still life classes I think you just apply....they give you the once-over and if accepted just put you on their books. If called they pay a flat fee per session.....
when I was at art college they used to advertise for life models, it was a modest fee at the time, more than minimum wage but not much more! you dont do a lot of hours
I have painted old men and women, although women models were quite a rarity.!