I think that to give this info a bit of validity, we should also include measurements! It makes a difference of when you start and how long you have been hobbying...and of, course, when you should stop torturing the providers! There are a few slim-and-trims that I would certainly not force to endure my belly-rubbin'!
Given a typical week or month, the rule says that the average age of a provider's clients that she has seen for the week (ot month) will average out to 54.