There are many in Manhattan. There is the Esplanade on West End Avenue and Atria on West 86th near Riverside Drive on the Upper West Side.There is also an Atria in Riverdale. There are numerous communities throughout NYC and the surrounding suburbs of Westchester and Long Island. New York City has a department for the aged with good resources and information below:
You appear to be asking in NY but your profile says you're looking in CA. Could you be more specific with a state and region where you are looking to find 55+ communities? Please re-post and clarify. Thanks!