More than just doing something physical, something group/team/class based like BJJ would also give the camaraderie and socialization that satisfied him.

I hear a lot of retired people say "I miss working", but when probed, they'll say things like "I miss the routine", "I miss the people I saw all the time", "I miss the structure". Work is not the only place you get these! Going to BJJ, kickboxing, clay studios, adult sports leagues, walking groups, some volunteer opportunities, etc., all fit the bill. I think some people put so much of their life/identity into work that they can't even imagine something else...