Speaking as a young monger, I can only partially verify what BB is saying. Most places are more on edge when a young man comes through the door. What you need to do, in this case, is just be confident. The more nervous and halting you are, the more your inexperience shows and makes the AMP residents nervous. Just act like you know what you're doing, though (and name drop a couple of places you've already been to) and you can get to the TS.
From there, it's all about being bold, but polite. Younger guys are at a disadvaneforum.xxxe because A) they're probably less experienced with the scene and B) they could be a trap, and still not look like LE. I ask you, what do vets have that newbies don't? Confidence. Confidence that they will get what they want and confidence that if they don't that they can leave. Project that confidence and it gets easier.
I admit that I have experimented with this. Granted, I've looked like I'm in my mid 20's since hitting puberty, but by no means do I look like the typical monger age. I've presented my age as everywhere on the 20-35 spectrum, played "nervous first timer," "long time vet who started young," etc. What works best for the young guys is emotional honesty. Nervous? Say so - you can be a guy who doesn't do this sort of thing often, and that often works great. That angle has gotten me FS at a few places that supposedly don't offer it.
TL;DR: Don't be an ass, be polite, but firm with the girl about what you want. Take the TS, chat, and be human