I don't understand why the questions are far below the radar.
Language is supported by intent, thus when I read hobby I interpret that word to signify something other than a competitive environment in this sport. Tossing the ball around is good exercise, and a lot of fun. However, you want more than that, I assume, because you mentioned that you want to throw faster than a 12 year old. So, all in all, that combined with
I can't access this knowledge easily because having grown in another culture it is something don't even know how to approach.
I gave you a source for accessing knowledge by suggesting a publication called TUFFCUF, published by Steven Ellis. I even stated : "Therein you'll find all the answers for getting to where you want to go". Simply access that publication on this web site, or, simply use any search engine on the web to access it by title.
Combined with your other statements, as dynamic as they are, my statement "below the radar" suggests a multidirectional approach to help you that's very unusual for someone your age. First off, considering your physical condition is kind of problematic with respect to advising you how to throw, then bringing that up to pitching condition. Throwing and pitching are at two extremes of the demands on the human body. Second, at 21 years of age, to be comparing yourself to a 12 year old's ability instinctively has me reserving any kind of advice, again, because of your low grade physical condition. I realize that you might not want to actually compete as a pitcher, only wishing to exercise in the training routines. But again, I'm cautious of taking that route for you.
All in all, there are some expectations that anyone with even basic experience coaching pitchers would expect when offering advice. In your case, those expectations were missing - thus my phrase "below the radar." Going one step further, I supported that phrase with my professional reasons. I apologized up front if that sounded rude and with any negativity, because of what I stated heretofore.
The best possible approach you could do, would be not to take advice, here or elsewhere, from those that know nothing about your physical condition, you health history and your lifestyle. Get the publication that I suggested, read it and determine for yourself how and when you should follow the basics outlined and go from there. There's a section in that publication that covers nutrition and conditioning for high school pitchers and that section might be just the things that you're looking for.