I would have to agree with people who have posted earlier. For your age i think it would be appropriate to get a light FR bike. I had to make a similar decision when buying a bike a year ago, i'm 15 and weigh about 60kg. I had a choice of a heavy downhill bike or a much lighter freeride bike. I decided to get a light FR bike for a good price. I think i made the right choice. I ended up getting a 2007 Kona Coilair which i am currently selling. I would recomend getting a Giant Reign, it's rather light and you probably couldn't go past it for value. Rather than just listening to us though, go check out your local bike store and test ride a few.