Biggest growth from first year playing

[Brees#1]

So I was listening to Rome today and there was a interview with Castellanos. Little did I know that he's having a big year so far because he changed his approach. It makes me ask this question because this could be the case with other hitters. When does the biggest change occur with a hitter(or pitcher) since he first started in the majors?

 

[TKOSpikes]

I would say there is no general number. It's all dependant. It's all relative. Coaches. Teammates. You name it.

I once heard the magic number for pitchers is 60 starts. I don't recall anything backing that up.