Can he continue involvement in a less manual way? (if he wants to) so, maybe not full time, but still has an input and interaction?
Or if he does want to retire, are there other things he can pursue? Any interests he has which he now has time to follow, perhaps there's groups that meet nearby? Or would he fancy volunteering somewhere? Or considering something like part time at B+Q or something, where maybe he can utilise the manual experience but in a less manual way, but with a belonging to a group
Even though work can be hard or get in the way, it does provide a beneficial structure. A purpose to get up in the morn and out of the house, some times we don't feel we want to or can but the structure helps us to cope better. So it would be good to work out what kind of new structure he feels would be beneficial to him
Can you have a chat with him, see what he's thinking/feeling, and chat about how, if he retires, he will maintain connection/interaction with others, how he will have a structure that will suit him. By forward planning can help the transition, and also may help to identify if anything isn't going well once the change has been made xx