Yes your grey is growing up.He is bonded to you. Take care never to re enforse his nipping by talking or picking him up. Any attention is seen as a reward to parrots, even shouting at him and putting in his cage. Just ignore it completely,and reward any good behaviour with lots of praise and attention.Make sure he steps up on command.Be happy that he likes his tempory care giver as it means if you need to, he can be left without worry .