Grammy, if they're unsocialized or have bad experiences, any dog can become aggressive or reative. You sure don't think of a Golden as having a mean bone in their body and they usually don't. But you're right....sometimes poor temperament and mishandling accounts for some of these stories we hear about lately.
SummerRiot gave good advice Snowruby. Get your pup in a class ASAP and get going on the sociailzation. Your time is running out where it will make the most difference. Be sure and don't react strongly to his reactiveness, don't punish. That can escalate the problem. Hope you get a good trainer who can help you with this in a proper way. Good luck.