Probably started soon after and shut down any chance of being taller than 5'8" to 5' 9". Probably the main reason so many of todays "bodybuilders" are below average height. AS supplementation sends a signal to your body that puberty has begun and this in turn sends a signal to begin the epiphyseal process and BINGO! You don't get any taller.
Doctors here can correct as they see fit as I am no physician.
I'm not sure if your reasoning is correct. You may be right but I remember Mike stating that he was taller than his father and I believe Ray was taller than Mike. Just like people criticize Lee Priest for being a midget because he juiced so early when he turned out taller than both his parents. Arnold was popping dbols like candy at 15 yo and it didn't hurt his height.
Also, during puberty, that's when testosterone shoots up and since all anabolic steroids are derivatives of testosterone I'm not sure how much of a role, if any, anabolic hormones play in stifling a man's height.
Also, I think men that tend to be short in stature tend to gravitate toward bbing and also are more successful in packing on muscle than their taller brethen.
Perhaps others more knowledgeable, like Van B, can chime in on this.