I heard about this initiative for housing students and the elderly side-by-side in the past, but this article just reminded me of one such program (it's still going on its small scale).
The "gains from trade" in this situation is that students get a rent-free room in exchange for spending 30 hours per month in volunteering to spend time with their elderly neighbors. The neighbors get the benefit of daily company and interaction that's far better for their mental health than occasional visits from care staff or family. The bonus from these interactions is that both young and old people learn more about the reality of their counterparts. Here's a TEDx talk by one of the students:
Bottom Line: Humans evolved in extended families that made it easy to exchange care for knowledge (and vice versa), and there's no reason why that should not be the preferred way of growing, aging and living.