I have two male labradors. The dominate male is 2 years old and the passive male (Buster) is 4 years old. The dominate male was neutered 3 months ago. The passive male (Buster) has become very aggressive towards the younger dog and obsessed with the other dogs genital area. The older dog has recently become very agitated if separated from the young dog. Is this a hormonal change and should I get the older dog neutered as well?