Kodak was 3 when I brought Kamari home at 10 weeks old and he hated her. He gave her such a hard time but she stood fast and claimed her space. They fought so much but Kodak was really mean to where I posted it here back then. LOL. Everyone told me to hold out, and he would come around. It took longer than I expected and they still fight of course but it had me to the point of giving one of them up.
But now, I wouldn't trade them for the world no matter how much they go at it. Good luck with your new puppy.