Too old.
Whoever he picks needs to be able to take the MAGA baton and run with it in 2028. At that point, Carson will be 77.
Doubt Carson has Presidential ambitions. He would be an excellent transition to the next generation of MAGA supporters.
Trump will have a say on who will be the 2028 nominee. Having Carson as VP with no presidential ambitions will liberate them both to make the needed tough decisions. I would assign Carson to take on the project to resurrect our cities. His experience as HUD Secretary will serve him in good stead.