J.J.
My son is 2 and he's been that way since he was little too. He's grown out of it somewhat now it just takes a little time for him to get used to someone then he's fine. Just give him some time he'll come around. Tell grandpa to steer clear of him at first and let him see you interacting with g'pa and that'll help him know he's not a "stranger". Most kids that are like this when they're little become the most sociable kids when they're older. Hope this helps!!GL