Why do some people say this about introducing male rats?

[spider pig!!!1]

If your male rat is 8 months old or older, it cant have another male introduced to it. But why is that
i mean i introduced 4 5 week old male rats to 2 1.5 year old male rats and had no aggression from them. i mean they still live together. one of my older rats died (old age) the other is still going strong at 2 years 8 months, and the other 4 rats are nearly 1 year old

 

[STEVEN]

I'm no expert, but I think it's because they will become competitive and it can turn violent.

 

[Cheyann]

Im guessing its because people think older rats will not get along with any rats which, as you know, is not true. I have never had a problem introducing male rats even when they are over a year old.

 

[Caty Levecque]

Sometimes older male rats can be extremely territorial. Not always, but it happens.

 

[Kuristaru]

Two male's will fight for dominance in the cage

 

[Catkin]

We've introduced young males to males over 2 years too & they've always been fine. The only time we haven't had success is when *all* the rats were adults when we began introductions.

So, I assume people only say this if both rats are over 8 months, or it's simply a misconception. Also, I imagine that that there have been some successful introductions of adult males.