When booking I was told "very young beautiful 25 year old". Always an understatement of course. And you ain't never going to get the truth out of the girls mouth.
Best practice is to look at their hands. A girls hands never lie. A beautiful made up face can't overshadow wrinkly hands.
Anyway, I'm a fairly good judge and I put it to girls often and they appear shocked at me either getting it exactly or pretty damn close (or offended if I'm one year or two years over haha).
Late 20s to early 30s real age max. If you want a 19 year old it's not her but if you settle with 'younger than most' you will be delighted.