what do you think where Ronaldo or Rooney played at the age of 20-21? or Gotze? you think Ferguson said "lets give Ronaldo (or Rooney) another season at fcking Bolton or Crystal Palace"? these players (i could tell you alot more players but i think you get what im saying) were not just squad players for their teams, they were key players. they turned out to be something great because their coaches trusted them even when they had good teams and could allow themselves to loan them out. thats how WC players are made.
i say give him a chance now and see whats he made off. if he has what it takes to become a great player he must prove it now. not prove it at Chievo, Sassuolo or a serie b team. he needs to come here, fight for his spot (in the start) in the team, take his spot, and put up good performances IN JUVE. if he cant do that there is no need to wait for him till hes 25. if he dont do it now he wont do it after 2-3 years in a average italian team either...