I'm a 43-year old provider and I absolutely ADORE older men!! I love the fact that mature gents are seasoned, patient, and well-mannered. You fellows know your way around a lady's topography. And most of all, I find that older men are much kinder and appreciative.
I don't have an upper age cap (my oldest client is 85, I think), but I won't see anyone under the age of 40.