I am also thinking about the city, including Brooklyn where one of my kids lives. I love Park Slope and it is very mixed-age (unlike Boston/Cambridge). Boston and Cambridge have “villages” to help people stay at home, and there are other organizations of volunteers as well.
I am a bit of a hermit. I am unsure whether this means a community would be good for me (socializing takes little effort) or suffocating . Right now, if I take a walk and wave at someone, that is enough socializing for me 
Cities provide a lot of people contact while allowing a lot of alone-ness. The corner store becomes an important part of your life!