A Dog's personality should not be affected by it's age, although Dog's often become calmer and tire easily as they get older. Your Dog's personality should stay the same, but your Dog will likely need to go for shorter walks and take longer naps.
it depends if you want to give your bull terrier some time
No. Two male Staffordshire Bull Terriers living together is a bad idea. They will fight each other, often to the death.
No, this will in no way affect the way your dog looks and is actually a very beneficial procedure.
At about 6-8 months old.
A Staffordshire Bull Terrier wins Best of Breed every year. Best of Breed is the Best dog from each breed, so there will always be one from the Staffy breed. This year (2011) a red Staffordshire Bull Terrier came third in Best in Group but a Staffy has never won Best in Show.
That would depend on whether your 4 year old is socialised with other dogs and used to other dogs, and also how you introduce them and make them used to each other. It is best to introduce them on neutral grounds and then see how they react to each other.
The American Pit Bull Terrier is the only breed that can be correctly called a "pit bull", but other breeds are commonly mistaken for a pit. 20+ breeds are often mistaken as a pit bull. This is why so many people get biten by "pit bulls" per year; because the dog was mistakenly called a pit because of it's looks, not because of it's actual breed. See if you can find the American Pit Bull Terrier; http://www.pitbullsontheweb.com/petbull/findpit.html
Staffordshire Bull Terriers can vary considerably within the breed, with some being described as ''short and stocky'' and some being described as ''long-legged and athletic''. Unless your Staffy is Kennel Club registered with pedigree papers, there is every chance that it may be a crossbreed with a taller breed such as a Pit Bull Terrier or Lurcher. This is not necessarily the case however, as some purebred Staffies are simply taller than others. My pedigree Staffordshire Bull Terrier was all-leg until she reached a year old and started to bulk out. Don't worry, every Dog is different!
Usually between six months and a year old, but it is different for each dog.
measure the neck of the staffy with flexible measuring tape in inches this should give you the size for the new collar
right now, in the UK, yes, definately. but as long as he has shelter and a few warm blankets(if it's cold), you can put him out at any time during the year, really.