My nephew is a farm boy, and he throws around hay bales and pick-up truck engines and renegade calves and dead deer and stuff like that. In his spare time he lifts using old weights that he and his dad stockpile down in the barn (but I don't know what, if any, "program" they do), and he used to do high school wrestling. I am SO glad he got out of that - the weight classes are crap and what he used to do to meet weight I personally consider stupid from the ground up, mostly because I am a more holistic kind of person and I don't think growing kids/young adults should EVER be fooling around with weight classes for any reason, except perhaps for medically indicated monitoring of some condition - but that is beside the point. Anyway, despite all the heavy work, he didn't pop until 17.
My brother is a machinist, now 42, part-time drag-racer, and throws around hot rod chassis and tires and industrial water pump parts and his itty-bitty wife (in a nice way

). He doesn't do much except live an active life (lots of boating - a favorite) and still he packed it on at 18, and not earlier, although he did avail himself of the weight room at our old high school some.
Gadsie, how tall did you say you are?? If you are already over 6 feet, dude, you have been growing like a weed, and you will need to be careful not to injure your growth plates and back! My Third (my third daughter - she is disabled and has muscular/joint issues among all her other stuff) has a pediatric orthopedic surgeon who is also a sports medicine doctor, and he is ALWAYS grousing about how young people get these crazy ideas about what is a Good Thing To Do and injure themselves; he should know - he works at one of the pre-eminent hospitals in the US and even treats Olympic gymnasts and other professional sports types. I had a friend at high school who got TALL early in his teen years, and did injure himself - despite his bone doctor's CLEAR WARNINGS - not to play basketball with the 18-year-olds because his extremely fast growth put him at risk for bone injury (he was told it would get better and that he could play basketball with the big boys in a year or two at most)... but he didn't listen, played b-ball with them anyway, they played for keeps, and then he had to endure total sports lockdown because of this stupidity.
I'm glad to hear that you DO backtrack and take care of yourself - smart kid, you are. If I knew how, and also weren't so internet shy, I would send you a photo of my brother at exactly age 15 - he looks EXACTLY like you, blond hair and all (we are genetically almost completely German, the rest is a smattering of Dutch...) - some definition everywhere but not huge amounts of mass, kinda' lanky with his height, but STRONG. If you saw him today, he is a rock. Same with the nephew.
My hubby was a total skinny beanpole in high school (we were dating already in high school), and despite an almost total intentional disregard for any kind of sports or exercise, I have watched him fill out just after 18 anyway.