I need to know...

So i got my Staffy son about 3 1/2 yrs. ago, love him more than anything!!!!! But I have to admit that i did not socialize him very much actually clearly not enough. I just wanted to protect him an in the process deprived him a very crucial lesson of his life. And i feel horrible about it.
Is it too late now to socialize him now?
Plus in the near future i would like to get him a friend, one of his own kind. There are very few and far between of his breed where we live. But i need advice and suggestions on how to introduce another dog, let alone a puppy to our no kids, one dog family. I already know that the new puppy has to be a female. But after that i need help!

Thank you - : )

Hi, do you have any training classes you could attend locally? That will help determine his attitude towards other dogs.   

Do you have an older well socialized dog he can walk with? You can also have him observe other dogs and then interact on lead. Seperate him if he gets out of hand.

As for the second dog make him part of the decision. Walk them together if possible and an article of clothing or blanket with the pups scent should be brought home early.

Great advice so far!
My parents Staff was never socialised and is now about 5 years old. The first few times we took Bane home to meet him it looked like there was no chance of him ever being sociable with other dogs, but now they get along great! Like best buddies!
It just took time for him to adjust to the idea of having another dog around. Obviously not all dogs will be accepting if they haven't been socialised, but as long as he hasn't had any negative experiences with other dogs there should be some hope

Never too old!

Do you know how he is with other dogs presently?

Could be he's fine. It is definitely possible to turn a shy/dog-phobic dog around, though. Puppy training is good. And, yes, agree - if you have a friend with a dog you can practice with. Dog of opposite gender might be a good start.