Try introducing him to another male first. Is there any breeders near you that can help out with this? Most male rats will accept other male rats without worry. I would suggest two younger males. Things always seem to go better with me when i introduce two newbies lol.

Getting him "snipped" is an option but i personaly dont think it should be done unless its for medical purposes. I have never had an issue with intro's though, expect with one boy who is on his own now. He is very old though and is our last male rat.