Personally mid to late 20s for me! My very first punt was with 25-26 and set the standard. In my experience, younger girls can sometimes be too inexperienced/starfish but of course this differs from provider to provider.
, an older Fijian Indian lady who I think was on the verge of considering me a bit young, the only good experiences with Brazilian prossies I've had have been with Alice Capella, who has to be well into her 40s, on her last visit to NZ but there are certainly plenty of women who aren't older than me who can at least feign enthusiasm about fucking a less than fit stranger.
Personally I like to do some pretty intensive kneading massage on women's backs and butts, preferably while they're riding me, and the older ladies seem to vibe with it more, so that's somewhat of a consideration.