Just like any of the other 'bully' breeds, miniature and standard colored and white bull terriers may develop dog aggressision up to two years of age.

It doesn't really matter how much you socialize them. Two years old seems to be the cut off for dog aggression. If they haven't developed it by then, then you're fine.

I know my dog trainer was working specifically on dog/dog aggression with a bull terrier and his owners.

They're nautural clowns, always playing and jumping around. I love them.