They are both one level away at ages 22 and 24.
Where they are now is extraordinary. The last step is to be able to think through what the team needs in any given game, and provide more correction. That is MVP level stuff, and I don't see any reason why they both won't get there.
Of course, Ainge needs to clean up this mess of a roster too. Its weird he's stuck now, because the superstars are the brutal part, and he's shown great skill at the smaller moves and balancing in the past. For some reason, he's been unable to do much positive in the last couple of years.