Weight lifting is a great way to start getting fit and healthy but alone I think it's pretty pointless, it's best to combine weight lifting with cardio work and a healthy diet as well.
I don't think 13 is too young to start, and the only thing you'll probably have to keep in mind is to not over-do it. Stick to weights that aren't overly stressful and won't put unnecessary strain on your muscles AND joints. A lot of guys I know try to be badass by lifting the biggest weights they can but in the end it does their body more harm than good.
Also remember that for every muscle you exercise with weights, you must also exercise the opposing muscle so that you are not unbalanced. If you do some biceps weights, do triceps as well. People forget that the triceps are actually a bigger muscle group than the biceps. If you do your quads, do hamstrings too. And if you do abs, do your back as well... etc.
I wouldn't take any protein pills/shakes anything like that to promote muscle growth. A balanced diet and health exercise regime will do more for your body.
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