Happy birthday. And, yes, it's normal for a man to slow down as he ages—it's not her—and there are younger men who take a long time to come. But such men need to take their partners' physical limitations into consideration. To avoid wearing out their partners' jaws, fingers, etc., they need to take matters into their own hands. They should enjoy that blowjob, handjob, twatjob, or assjob, take breaks to stroke their own dicks, eventually bring themselves to the point of orgasmic inevitability, and end by plunging back into that mouth, fist, twat, or ass to blow their load.