As a beginner, I would recommend something cheap. Think wal-mart. As a 13y.o. you likely have some growing left to do. The bikes that can be purchased at wal-mart are decent, and don’t require a ton of maintenance like the high-end ones do.
If I were you, I would get something that you like at wal-mart. Really, anything will do (so long as you fit on the bike): you are just learning; make sure you are comfortable with it. If money truly isn’t a problem, buy something more high-end as you get into the sport more. You will have a greater appreciation for a better bike after you learn your stuff on something more – disposable.