No question there is a big market for 18-22 but I can't do it if I'm to be honest. Just doesn't feel right and, while I can see the hot, I can't get interested. For that reason my starting age is around 25. Give me a hot 35 yo who is into it and I'm down.
When a 19 yo comes up to me in a S/C the idea of a lap dance strikes me as laughable.
The age I liked as a teenager was 25-39 and that range has never varied. If I saw 19 yo's I'd have to get two so they would have some there who knows what they are talking about.