Labs are a gundog breed so like to be given a job to do, if he has still retained his guide dog training then keep giving him tasks to do. Retrieveing games are something that most labs love also anything to do with water.
One of the most important things in labs is to keep their weight down, you should be able to feel his ribs with a light touch but not see them. Labs are very into food so keep him occupied with a stuffed kong, chews, use his meals for training or scatter his food in the yard for him to find. Regular exercise is also essential.
Older labs can be prone to joint complaints so consider adding glucosamine and chondroitin to his food and keep and eye out for signs of hip and elbow dysplacia and arthritis. Also keep and eyue out for ear infections, the shape of their ears means they are prone to them.
Good luck and enjoy your new friend!