Rats just wont get along?

I have two male rats, one is about 5 months and the other is 8 months. I've done several things to try and get them together in the same cage but nothing seems to work. When they fight it is horrible. My younger one's fur comes out and my older one just keep pestering him. There are loud squeaks that comes from my young one. I've tried everything, vanilla, putting their cages next to each other for 3 weeks, switching them to each others cage. Nothing seems to work. I'm thinking that they just have to be separate because once they see each other. My older one goes to groom my younger one. The young one stands still for a second then squeaks then bam fight. So please help me. Are they still just fighting for dominance and should i let them duke it out ((I always stop them once i see fur coming out, or if the fighting seems really violent)) or are they destined to be alone at this point.