I have a 5 month old male, Wally, who is healthy, intelligent, and gets on well with his slightly younger cage mate, but he is bizarrely aggressive toward my 2.5 year old. He has it out for my sweet older rat that I love dearly, and is stressing him out so much. Vets in my area willing to do neutering charge more than I can afford. After several injury issues, I currently have them in separate cages which is denying my older rat the ability to be with the other small rat too since I can't get Darwin out without Wally running out with him. Initially Wally was also prone to biting me, but I've mostly socialized him out of that behavior. However, he's only getting worse to my older boy. He could really benefit from being in a home with someone more experienced in rat behavior, has more cage options on possible companions and/or who has a vet that will neuter for less than $200 (which is what mine is looking to charge when all is said and done).