This notion that weightlifting shouldn't be done by young individuals because it can lead to stunting growth, are completely insane, and unfounded.
I can use myself as an example, I started weight lifting (snacth & clean and jerk) when I was 12, and now as an adult (24 years old), I'm 188cm (6'1) and 140kg (320lbs) at around 10-12% body fat. I don't believe that makes me small, or had my growth stunted by any means.
The reason for this, is that the body can't tell the difference between you lifting weights or going through normal life struggles, and the human body works in a way that it adapts over time to stresses put on it. In a more natural environment (think "caveman" times), I believe it is easily imaginable that a person aged over 12 would have to do some physical work, and carrying, be it to help with hunting and harvesting, or just manual chores.
The problem with weight training as a younger individual is training properly. When someone is new to something, and it being a physical activity, injury is at high-risk. That is why it is very important for younger trainers to be taught proper lifting techniques/form. Also, it is during these years that a person will learn tendencies they will continue to do throughout their whole life time, so it is important to be taught right from the start.
Furthermore, when you are younger, it is the time you will see the most growth you will have, and thus, probably your biggest strength gains. Training during this time will help build a foundation for the rest of your life, and shouldn't be easily dismissed.
Also, if you need some real motivation, something to see, here is a 13 year old girl from Russia that can bench 110kg (242lbs) under competition rules.
Stop being out done by little blonde girls.
[video=youtube;bxAc97K2I5M]http://www.youtube.com/watch?v=bxAc97K2I5M[/video]
Also at 2:27 of the video, you see her pose with other people.. who are full grown adults, and she is taller than most of them, outside of Mike Jenkins (who is 400lbs+ and 6'6), and 2 other guys, so stop the bullshit about weight training stunting growth.