Sammy, I am not in full accord with the Dr!
if you want to hit the weights that's great. My pop took me lifting when I was 12! I really enjoyed it. I got stronger pretty quickly (mainly conditioning) and just became a better all round sporty kid. I didn't pack on much muscle but I now understand that it was a combination of things. As a kid I was very active (as I'm sure you are too). There were no such things as PS2s so I was always out biking, skateboarding, climbing, whatever. In order to put on muscle you have to eat a lot (best not to eat junk too) and it may be that your daily activities and testosterone levels at present will prevent any great gains. However, you will see a difference and you also have the benefit of sites like this to guide you.
I now have a 12 year old son and he's going to be starting some lifting this holiday. Nothing too strenuous. 10-15 reps of each exercise and, very importantly, I will be teaching him about each exercise and helping him to learn good form.
So, start off learning to do the main compound lifts like squats, deadlifts, bent-over rowing, chins, dips, bench press, shoulder press (and some biceps curls and triceps extensions if you like) under supervision. Try to keep your w/o to a half an hour or so three times a week. And do this for a few months, keeping the reps to around 12-15. Once you are happy with the exercises you are doing you could do a kind of HST. Start a cycle with 16 reps per exercise for 2 weeks, then two weeks of 12s, then 2 weeks of 8s. It's fun to change the rep ranges and lift a bit heavier but you need to have good form first.
I am sure the girls will notice your efforts but results don't come quickly. If you start now and keep it up throughout your schooling you will have built a pretty good physique by the time you are 18.
All the best!