He played at least 5 years in the Cardinals minor league system as a hitter. Never made it as a pitcher, even in the minors. A big mature kid at 12 isn’t a guarantee that he’ll stay ahead of other players as he ages. There’s a reason MLB players usually look younger than their years.
And many players who might have been greats have undergone some hard to cure physical damage that ended their careers, especially in the past.
He could have if he had proper mentoring as was explained by teammate Tom Paciorek who was signed by the Dodgers and played for then new coach Tommy LaSorda......
It was the expectations thrown on him due to his success in the teen years that he wasn't able to deal with once signed by the Cardinals..........
He was a diamond in the rough that could have blossomed had he had proper leadership. Unfortunately he didn't and he ultimately walked away from the game. What is most telling about his mindset at that time was the fact that once he returned home, he threw away every single item of his history, from the trophies to all the magazine clippings he and his family had accumulated and never played baseball again.