
It is never too late, but if you have no experience then I would not venture to a show as an exhibitor until you have trained your dog for what will be required.
If you phone the Kennnel Club and ask for Ringcraft training classes in your area they will send you a list.
Your dog will have to accept a judge looking in its mouth, feeling all over it's body, including the testicles if male, lifting feet etc. He will also have to learn how to trot steadily at the right speed on a loose lead so that his gait can be assessed, and then stand in a pose at the end.
Dobie classes are usually large, so he will have to cope with running around a ring with a lot of other dogs without being distracted or frightened/cross with them.