Its amazing to think that someone so young can have it but I would say that Nathan surely has it already. He is almost 5 months old and he has more personality that some adults I know.
He will smile at you, sometimes just because you are looking at him. He will give you this shy guy type smile sometimes that is just wonderful to see.
He grunts when he doesnt like what you are doing.
Nathan is starting to be really fun to be around. I hope that lasts forever. :)