Crowds, concrete, and occasional polar vorteces excluded, New York is a real retiree’s town. (That is, of course, if you can afford it and are in relatively good health.) Can your friends down in Fort Lauderdale catch a half-priced matinee at the Film Forum before taking the 7 train to Elmhurst for Indonesian food? Those looking to keep their minds stimulated have dozens upon dozens of classes to choose from�the history of male ballet at Juilliard, conversational Italian at the 92nd St. Y, wood-carving or figure-drawing at the Art Students League. And for the lucky ones who happen to live in a NORC (a Naturally Occurring Retirement Community, of which the city has hundreds), sometimes getting your culture fix is as easy as heading down to the lobby for a weekly show-tunes sing-along. (And don’t forget those discounts�on theater tickets, museum admission, and Fairway hauls.) What follows is a case for sticking it out in the city: from the restaurants that are miraculously both buzzy and not too noisy to senior dinner-and-a-movie clubs to the potential JCC hook-ups. (For more on the joys of aging, see "65)."