Bethenny Frankel is clapping back at the haters who say she’s too old to wear a bikini. The former Real Housewives of New York City star, 53, has been showing off her toned physique all summer, baring her body in swimsuits as she enjoys plenty of poolside time in the Hamptons and holidays at the beach in St. Tropez, RadarOnline.com can reveal. In a video posted to Instagram on Thursday, Frankel twirled confidently for her 3.4 million followers while rocking a black and white bikini, saying: “Many of you say at a certain age you’re too old to wear a bikini. This was in my drawer and it has tags…