I'm in my mid-twenties and started a couple years ago, I used to email this sort of thing to them, "I am quite young...etc", I started off my punting career looking for older women, that was my fantasy at time so I thought it was quite relevant to tell them I have a "hey teacher" kind of deal going. I do look quite young, usually ID'd at Bars but now I don't bother. As I am slightly older and slightly wiser...
Way I see it is they need cash and will fuck for cash, I have cash and will depart with said cash if they fuck me. I look at their profile, if there is nothing about an age requirement, then as far as I am concerned, it isn't an issue (I would say 18+ is a given for the majority).
Scan their profile for this, if it isn't there, assume it isn't an issue and ring them/text them (I prefer not to email myself) your requirements and go from there. Couple times I turned up and I was asked if I was of age, even one wanted to look at some ID, I wasn't too bothered about my personal info as I knew it meant fuck all to them who I was but if you're ever concerned I'd say just hold it up to show your D.O.B, cover your name + address - Most won't bother to ask anything other than "are you over 18?". To which I reply the truth "yes" and then we're on.
I advise you do the same, though if you're looking for younger ones, the one or two times I've punted with a lass my age I found they probably preferred an older dude for their experience. I personally leave the younger ones alone, I still think I got a chance to date a few for free until I get a bit older.