Probably, Pogba is overrated. But you lose credibility when you say stuff like he is 'very average'. Pogba's technical skills and output stats, even this season, cannot be considered average, never mind 'very average'- whatever that means. When you say stuff like that, it begins to look like you see him through a twisted lense; you do not see him for what he is.
As for the 18-22 theory: on what basis have you come up with this age range for development of critical skills? Why not 19-23, or 17-21? Is it because 18-22 fits in with Pogba's development trajectory and time in Italy? Furthermore, are you really suggesting that, once developed, players can't make adjustments to adapt to a different pace of play? What does this imply, then, if, for example, the manager decides to change style of play? That it will never work with players over 22?