Aggression can begin to develop between 9-12 months of age.This is due to the beginning of sexual maturity and hormones.
There is another phase you may see aggression come out again. Around 18 months (late adolescence) you may notice more assertion, independence and aggression.
By two years of age most dogs will have shown their full extent of whatever aggression they have in them. You want to get help from a professional CERTIFIED trainer if you have concerns.
You can have a darling puppy but then end up with a tragedy on your hands. ALL breeds and ALL sizes can show signs of aggression.
If you are having behavioral problems with your pet, please contact Aunt Penny for a private consultation. Call 724-515-7790 or email firstname.lastname@example.org