Rooney is 30 in October and has been playing at the top level since he was 16/17 and I suspect he isn't the most naturally fit player in the PL. If any player is going to burn out in the next couple of years it's him.I don't understand people saying they need a top striker. As much as we hate him surely Rooney fits the bill and will actually play there now they have a midfield - they need another striker but not a stater imp.
They do desperately need a top CB though if they want to challenge. Even then they'll be bedding in a lot of players so probably won't be top drawer this season. People underestimate the value of a settled squad - it's one of the reasons Ferguson had so much success with some mediocre players playing major roles.
United should be looking at a Bony/Remy level striker, not Muller or Kane.
A top CB should be their priority, I'm not sure it is though.