As long as a girl is an adult (18+) from a reputable agency, I don't consider age to be a very important factor. I choose more by description, photos, experience (time in the business) and reviews. All things being equal, older girls tend to be more mature and I tend to choose them. But I have had a few great experiences with girls advertised as 18 or 19 and a few mediocre experiences with girls who are listed as 25-30+.