I have a 9 year old male abysinnian who will spend a good 20 mins a night sitting next to me and paddling away on my thigh (he doesn't suckle) but he does dribble!
So in answer to your question "will he grow out of it" .... probably not!
As Monty is paddling on his sister I would recommend you keep their claws trimmed (just clip the nasty razor sharp points off) this way it won't be uncomfortable for Callie