Firstly, I'm not the best on here to comment on "Club" game but I don't see it as vastly different to game in most social situations with larger groups of people around.
Whilst you see all the other guys as competition, which I agree they are, they are not trying to compete with you directly. Girls rarely go out to "go home with someone" in which case you are competing with other guys. Girls go out for a good time, if they meet someone they like enough to go home with then great, but they have a standard unique to her and that's what you have to meet.
The more mature guys, as you put it, will have a more relaxed confidence about them. They know what they have to offer her, so when they are with her they give her "good feelings" from a fun interesting interaction, and a that's what she remembers. They have their eye on the ball, open her, hook her, isolate and take away. They will probably open a number of girls before they get the hook, but they will read the signals quickly if she's not interested and move on. The fact that they will move on can often trigger a girl to change her frame and take the hook, so she doesn't lose the interesting fun guy she's been chatting to.
Younger guys are often very "try hard" and "hang in there" and persist which is fine to a point, but she will see this as very "try hard" so you also need to value you time and effort and move. Give them an opener and a couple of minutes then say, "it's been lovely chatting to you, but I need to get back to my friends, perhaps we'll catch up later" and appear to be going to move on. I've had lots of girls that then immediately try to re-engage before she loses your attention. Sometimes I'll chat a bit longer, sometimes I move on. If she's still giving signals she's more than interested so worth returning to later. That doesn't mean hours later, although it could be, you can be back with her in 10 minutes and you'll find she can me much more receptive second time too. When you have a room full of girls to chat to don't get hung up on one of them, repeat and rinse this process to sort out a number of prospects. This can also make them chase too as girls can be quite competitive when they see a prospective guy they like chatting to another girl.
Just because you're 20 it doesn't mean you can't act and dress a little more mature like a 25-30-year-old. If they ask your age deflect it. Girls usually ask your age either as a general question so deflecting it is fine, or they want to use it as an excuse to say "no" which means you've failed to set up an attractive frame anyway. Half the girls I've taken home have never asked my age until a second or third lay anyway. Admittedly I'm on the other end of the spectrum now, but the point is you're not competing with the other guys really, you need to show you can meet her desire for a fun time. So, you need to change your perspective and mindset and things will fall out better for you.
