Commendable, all you young guys already looking to get involved in your fitness. I was in a very similar situation when I was that age. My doctor did indeed scare me off weights a bit for the reason of stunting growth but hey, it was 15 years ago and I'm sure his intentions were good.
Any how, I think the single greatest thing I did at that age to get in good shape was indeed
EAT. The summer between 8th and 9th grade I decided I wasn't gonna be scrawny anymore and went at it like a mad man. For example, breakfast was generally 2 servings oatmeal, grapefruit/apple/fruit of some kind, 16 oz. skim milk, vitamins, 96 g egg protein shake (GAWD awful tasting stuff, I doubt it's even made anymore YECH!
). Egg protein is excellent though and cheap. Tuna is a good inexpensive option as well. If you can spring for a good shake though that's the way to go, I know they've come a long way from the vomit stifling sludge I inflicted on my young self
.
Then I rode my bike a couple miles to the gym, free weights for a couple hours, back and legs got there own exclusive days, i worked other groups together. Then lunch; 2 ham/turkey sandwiches, carrots or something, yogurt, more milk (bowl of cereal maybe), more coagulated egg protein lol. Then back to the gym for some swimming. In those 3 months i went from about 130 - 155, and cut my body fat dramatically at the same time. When I got to school the next fall people could barely recognize me. I'm convinced eating a really good diet, and eating like a horse too, with the training is what did it. Take out the diet and I probably wouldn't have seen much change I believe.
Oh and yeah, the weight you are using is a tad light I'd think. What I did was, one warm up set - bout 50% max weight, 12 - 15 reps, pyramid up with 2 8-10 rep sets, one heavy 4 - 6 rep set, another 50% weight set. Then I would do a 'burn out' set where I dropped the weight to about 2/3 max and went to failure not even counting reps til the muscles were on fire, then I'd try to squeeze another 5 or 6 once I was in pain. I looked to add some amount of weight to the bar every couple weeks or so generally. I am not educated in physical training though, that's just my unprofessional little routine, it may not be advisable for someone your age so don't take anything I said with out checking with someone smart
. On the diet though I am pretty certain.