I assume the third floor condo has elevator access? If not, then that's a major consideration for aging (obviously).
South Kingstown is very accessible to Providence and Boston by train. Shorter drive to Wickford Village or Mystic Village in Ct.
Plymouth is served by the MBTA.
If money is not a major object, then it seems that your choice is going to come down to what you like best. There are other nice options as well.
Have you looked at this one? Gorgeous water views.
Villages on Mount Hope Bay Waterfront Homes Providence Boston Newport
Short drive to Newport or Bristol.
In my neighborhood, if you have the dough, you might go here- it's in a woodsy setting but very walkable and 3 min to shops and restaurants and all Providence has to offer.
https://www.laurelmead.com
If it were me and I were single, I'd just buy a condo in a town- not necessarily in a retirement complex- since they are often built where there is (was) more land. But not 'til I'm 75+.