I have answered this and I don't especially want to keep hijacking a Dozier thread, but I'll answer again. It has nothing to do with age, it has to do with the fact that Meyer has two specific things to work on - developing a passable third pitch and improving fastball command. If he can do that he is an ace. He is not there yet. If he is called up he will have some success and some failures, mlb hitters will learn how to exploit those two shortcomings. If he fails, I fear he will fall back on his stuff moreso than keep on developing the two things he needs to work on. I would personally love to see Meyer pitch for the Twins, sooner the better, it might even get me to a couple more games, but I can accept a patient approach here knowing the payoff might be bigger down the line. All this to say that despite your attempts to generalize this, my thoughts are unique to Meyer in this case.