Vlad Guerrero Jr. is the best hitting prospect in baseball over the past decade and could likely enter the majors right now and hit just fine. Follow him in AA for the first three months if you want to follow a high level prospect, but he'll be up soon enough.
He'd probably be an average major league hitter this season, as Trout was at 19. Wouldn't expect him to be good, though; the list of guys who have been above average hitters as teenagers in the past century could be counted with Mordecai Brown's pitching hand. Nor do I think they will/should be calling him up in 2018.