He is supposed to be 23 years old this year so another 3 years would be 26 years old for him, thats a pretty ripe years for football players to move in to another league. He is going to be freaking rich and for the next 3 years if he play well then he will still be on the radar for some other top club out there so its pretty much the 'best' decision that he made to stay with PSG ( and be a freaking rich by milking the club  )