I'm not sure how much that is age correlation. Suburbs are older and usually have more parents, so they're more likely to volunteer in clubs and organizations. Even in my urban area the most frequently volunteered at organization is the PTA and most of the soup kitchens and senior centers have volunteers in their late 30s to early-50s.

Community engagement isn't also quite the same thing as friend groups. This is making me interested in doing a similar analysis.