The youngest you can start a dog in actual conformation points competition is 6 months. There really is no age that is 'too old' to start them, or finish them

Some people don't debut their dogs until well after they're a year old, possibly older. Most of the time their reason is to let the dog mature and fill out some. Some dogs are good from the beginning. I heard recently of a bitch that was, I think, 6 years old when she finished her championship. My breeder had a bitch they bred(and co-own) finish her championship last year at the age of 5 years old, after about a 2 or 3 year hiatus and a litter of puppies! So, no I don't think there is an age that is *too* old to begin them. I do think that after a certain age, though, that they're considered veterans(if they've finished). I'm not very sure about the veterans part though, so maybe one of those who know could inform!