I can empathize, I am 6'10" tall and was about your size when I was 16. It took the rigors of making a varsity football team that had multiple state championships and a coach that respected my hard work to get me broken out of the realm of the skinnies.

It takes some serious training and strict attention to diet to pack on weight at your age and size because metabolism tends to be through the roof, so here are some pointers...

First of all, ignore the punks in your jail. They are there for a reason and they'll give you shit no matter how big or bad you are. They don't have anything better to do. Feel free to remind them of that and that you will be going home at the end of your shift if they get too lippy...

secondly, what are your diet and training regimen like? Just to say "I want to buy this product will it help" is not enough useful information for us to give ya some assisstance achieving your goals of packing on 20 lbs.

third, are you willing to work for it? Can you set a goal, learn what you need to do to achieve it, develop a plan and stick to it?

That's the most important thing you need to be a bodybuilder.