My guess would be the preference is less about appearance and more about demeanor, but of course I could be wrong. The difference in age, for me, typically means that a gentleman over the age of 35 will be more respectful, have a better idea of what he likes, and will be less likely to say or do offensive/completely disrespectful things without even realizing it. Age tends to bring a bit of grace & wisdom for people of both genders. Thats such a gross generalization though, and... I'm rambling.
My point is that I'd not hesitate to contact SPs and explain your situation, your ideal session, and see what comes of it. You may find it IS all about appearance & won't work, or you could find yourself with a better understanding of the particular woman & an appointment to boot. I'd be surprised if anyone's going to card you, particularly if you're up front and communicate with them ahead of time.