Advice on getting a dog castrated?

I have a male staffordshire bull terrior who's nearly 7. Im just looking for advice really. Iv heard that its good to get your dog done after a certain age as it can help them not catch certain things and maybe have a longer life. I also wanted to know if there is any side effects from it, ie will it change his personality and things like that. I would be very grateful to any answers you may give. Thanks.