Well man you dont have to wait til your 21 to be a pua lol, another good thing about natural game is that it aplies to other situations other than in night clubs like when your out at the supermarket or at a college party ect... and not sure where you live but most places you can go to clubs when your 18 you just cant drink.. which honestly you dont need to anyway.. but on to material if you have and ipod or iphone then i highly recomend going into itunes and downloading the pickup podcast, its free its full of content and its helped me out in game more than any other material ive used, it covers every aspect of natural game, if your looking into buying a good book then go here
http://howtotextgirls.com/400/
its called the txt book, it covers everything from how to get a girls number to settting up dates and pretty much everything relating to txting lol, that should definatly cover any problems you have, it will advance your game to a whole nuther level, its what i started out with and really works, let me know what you think:)