Between 20 and 40, age and looks are far less important to me than attitude.
A pleasant girl with a happy smile and a happy, enthusiastic service can be any age and still be high on my list.
In fact, I have found in my limited punting career that younger girls are much more likely to give a poor service for a number of reasons - they don't like what they are doing, and only doing it for a few fast bucks, and so their hearts are not in it.
Or they set lots of rules - "don't touch me here or there ..."
Or they think that because they are young they can set any price and blokes will still pay (actually they are right - the first time !).
Or they don't treat it as a business, and therefore take the logistics seriously - checking emails and SMS, double booking, cancelling at the last moment because they are with friends and don't want to leave to come to 'work'.
Or ......
My preferred age group is between 25 and 35, but I'll met some nice ladies on either side.
Cheers.