Of course people can change or mature and become more of a well rounded individual. I just don't see Rooney being able to become a brilliantly minded tactician.
He has worked with Ferguson so no doubt could man manage and motivate, but his lack of dedication to his physical well-being points imo to someone whose not suddenly going to dedicate himself mentally to becoming a top level or even lower level manager
I think we massively overestimate how intelligent these managers are, again in terms of the sort of general intelligence measured by IQ tests and so on.
Ferguson probably wouldn't perform very well in a logical quiz, yet he was one of the most successful managers ever, and his longevity on the top was unrivalled. He was an absolute master of how to play mind games, he knew exactly how to motivate his team, he knew how to delegate, he knew when to get rid of players (but the one time he tried to be clever and use data, he got it horribly wrong).
None of it requires that sort of intelligence. It probably doesn't hurt if you've got it, but I think it matters far less than we'd like to think. (This is also true in many other walks of life, but that's a different story.)