Yes your muscle mass will become great but you can still lift weights. I honestly don't undertand where ppl get the idea that weight lifting will hurt u. JUST DONT OVER DO IT!! Other than that wieght lifting is perfectly fine at 13.
and sometimes the place i'm at is at a loss for words
if i think of something worthy, i know that it's already yours
and through the times i've faded and you've outlined me again
you've just patiently waited, to bring me back and then ---Relient K "I am understood?"