With many breeds (Labs being one), 2 year olds are still not fully mentally mature. You squander some of the dog's potential by not starting them as early as practical, but there's plenty left at 2--assuming the dog has some.
Start the dog off like he was a new puppy with formal obedience, and use a structured, sequential training program. Things often take longer with dog that's had a couple of years to develop bad habits and be his own boss. Be firm, be fair, and let the dog show you when he's ready to move to the next step. If all the hunt hasn't been bred out of his line, he'll be great.
