Wow LostinParadise, I’m not sure how to answer this. Should I go serious or funny?
Are you presuming that all people around the world reach this age, or that it is related to income and access to technology? Is this now, or in some future? Would everyone reach this age, or would there be the drop off, as there is now?
Your idea about marriage contracts and career changes have been standard tropes in science fiction for decades.
I guess I think we should look at the old old now; those who are healthy, of course. I think that the old old would be seriously invested in “mind exercises” as a way of keeping their minds from decaying. There would therefor be a lot of math game societies and chess societies, and research institution that are designed to, a) give the old old a chance to learn new skills, and b) help the world solve current problems. In addition, tons of people would go back to school. In fact, people would be going back to school to retool about every 10 to 20 years (this will happen, anyway).
I think exercise companies would be big, in an effort to help the old old keep their bodies in the best shape possible. Almost all of them would have a lot of replacement parts in their bodies, because our joints just aren’t built to last that long. They aren’t even built to last to 60. This means there would be a big industry in joint replacement, and other bionic parts.
I think the service industries would grow hugely. These people would need a lot of services, and also be able to afford a lot. I don’t know where the workers would come from. Immigration from countries that are very poor? More children? Maybe there would be mandatory service for everyone from age 25 to 40. These folks would do the service work. When they hit 40, they could do what they wanted.
I think you’d see that the most desirable areas to live were populated by the really old, and the younger you got, the more you’d live in scuzzy areas. The old would probably hire tons of security to keep the young from stealing stuff from them, or revolting against the established order. The youth crime syndicates would grow powerful the favelas and inner cities, and the old would never venture there. The tensions between young and old would be exacerbated way beyond what happened in the 60’s.
Oh dear. I’m going dystopic. Let’s think of good things. Hmm. Technology would advance faster and faster, making it possible to confer more advantages on the young, who would stay in education until they were 40. The elders of religions would try to keep religion in the old style, and youth would be starting new religions, one after the other. Daloonism would most likely become the largest religion within 100 years (the original daloon being long dead).
Anyway, I could go on, but I won’t. That’s enough.