"social engagement" would not be increased with living in rural green areas, it would be decreased. That being said, I recover mental energy from being away from people so the original point is true that being in green areas would benefit my health and stress levels.
The folks I know that stayed young into their 80s and 90s were ALL gardeners.
Not true. Small towns and rural communities have more socially MEANINGFUL interaction. Cities encourage social anonymity. Many people in rural areas bitch about “all your neighbors know what you do”.....but that same snooping neighbor is likely to be the one to call 911 when you fall off your roof, or check on you when you fail to “follow your usual routine”. I’ve lived in both environments, and rural/small town is WAY preferable.