I started with the sand weights at 13, but started with push ups and situps around grade 4. By 9th grade I could do 600 pushups non stop. I know most people call BS, but it is the truth. I was extremely OCD and felt the need to start doing pushups every morning by 0605hrs. I woke up at 0600. By 9th grade and the 600 pushups I was 5'5 135lbs of shredded muscle.lol Actually funny because I had pec striations and probably 4%bf. It was then that I used olympic weights for the first time and shortly after gave up on pushups. By my senior year I was 5'7 175 lbs at 5-6% bf and could bench 350. At this point I only benched, curled and did pullups. I think when someone starts young and hgh llevels are high it somehow changes your natural limit. Almost everyone I know that started early seemed to have an edge. Sad thing is , it took me another 20 years to get up to 230 bw and a low 500's bench. I guess I started off strong, but after looking back, it took 20 years to gain another 50 lbs of bw and gain 180 on my bench. During that time I experimented with just about anything I could and never really noticed any huge gains. Maybe a plateaued early. Never went crazy, but did several cycles over the years. Now at 40 I am heading the other direction after several injuries:torn labrum, rotator , back and neck etc. I guess now I am only about 100 lbs over where I was in high school strength wise and am on hrt for life.
Thought it was a good story, but to answer the OP question. 27 years!!!