like targon said most therapy organization will have you wait until they are a year old but training needs to start as soon as possible. I feel like a therapy dog should be fool proof. There is so much going on at a hospital or nursing facility that you need to have a calm and obedient dog. I do therapy work at a local nursing home and they have a resident cat...my dog doesn't do well with cats but he is obedient to me and does not listen to his instint of chase when in the nursing home.
Also with a large breed you want to make the best impression because there are people with dog fears and if your dog is unruly it makes for a terrible impression.
Training should be done to socialize your dog with every thing....take your pup to stores, parks, kids soccer games, etc...
And most important have fun.
