As much as I love baseball, I've always thought it wasn't a very hard game to be a manager in. Basketball, soccer, and football would be much tougher to coach. In baseball, if you teach the athletes the fundamentals and some strategy, you can kinda just sit back in cruise control and take some motivational speaking classes in your spare time.
In reality, coaching any sport is not an easy thing, even at the lowest levels.
However as kids get older, they become less willing to listen to instruction because they already know it all.
I think we're confusing two different aspects of the game. Managing a professional team is much different than actually coaching the team. Sometimes the duties of the person can overlap, but in this case, Jake the kid is handling the day to day management of the team, ie. payroll, hiring, firing, trade negotiations, etc. Jake has a coach that handles the aspect of getting the best out of the players that he decides should be on the team.