There's a curve. It's kind of an upside down bell curve.On the high end, 18-21-year-old "new girl!", expensive, shitty service.
The 30-year-olds who've been doing this a while, give good service, reasonable price. Best value for the buck.
The 40-and-over's (sure, they say 30's, but their stated ages are all lies) who have been doing this for 10 years, charge a LOT of money, getting up into the same price-range as the 18-21's, but they give outstanding service for what you're paying.
Now, this is mainly for FBSM, which is how I roll, but when I used to do F/S, I remember the same kind of pattern applying. The girls that were about my age gave the best value. The girls who were older than me took the top of my skull off-- insanely good, but the best ones were pricey. The girls who were younger than me were hot as fuck, but expensive, flaky, and gave shitty service.
Nowadays I go for that mid-range-- girls about 10 years younger than me-- but if I had money I'd go for those my own age; they are the best.