I mean, can't be growing a bit in perks case
Well, there's a bit of a difference between Perk's and LeBron's growth. Perk's rookie year had little, practically no garbage minutes, of actual playtime. The year was little more than time for him to do upper body weight training and lower body aerobics, during team practice drills. As a result, within a year and half, he was Perkules and that would actually fit his workout profile. The recovery time matches what he was asked to do, for the 1st year. I'd seen this with sedentary office workers, who only lift, and don't take to the running/rowing regimens. They become stocky but don't have much cardiovascular conditioning.
On the other hand, LeBron's been constantly working out, since his start as a franchise player, esp in cardiovascular as well as overall strength training. All and all, that type of schedule, makes one lean and sinewy, not bulked up. Also, if one used HGH, it rapidly metabolizes into IGF and other subhormones which then assist in rapid recovery. It's not a analog/derivative of testosterone which is easy to test for. HGH disappears in the system, within an hour; and even its subsequent metabolites don't have lengthy residence periods.
In a way, it would have allowed LeBron to make incredible changes, in both his bulk and durability, for his first couple of years in the league. I wouldn't be surprised if someone discovers that he has a stash somewhere but then again, you can't really *test* for it, unless you entrap him.