The oldest for me was 74, and the youngest was 18! I tend not to like the younger clients, I have nephews, cousins that are that age, and I just feel funny with anything under 25.
When I worked in Amsterdam, I would check IDs, if I suspected they were under age.
I have had a 15 year old call me one time from a land line, I scared the living shit out of him! I threatened to call back when his mother and father were home, and threatened to tell them completely what he was up to. I think he shat his pants. I never called, of course. But he stopped calling me though.