Always reintroduce training to your dog. Make it fun. Make him think. Help him to enjoy being a well behaved dog. You will never regret it.
Older dogs can begin training as soon as they have settled into their new surroundings.
Remember to introduce new things to your dog slowly. If you have to wait 4 weeks to begin a formal training program, that is fine. Continue to work with your dog on a daily or weekly basis. A dog at any age can be taught whatever you choose to teach him. As I have stated before, there is no substitute for a well trained dog.