Alex Rodriguez has been living in a luxury rental apartment on the Upper West Side while he continues rehabbing after hip surgery, reports The Post’s Jennifer Gould Keil. The apartment is at The Aldyn at 60 Riverside Blvd., which boasts a world-class gym, the main reason he’s living there. “Alex is spending his days in rehab. He’s at the gym for two hours in the morning and two hours in the afternoon, trying to recover as fast as he can so he can return to playing ball for the Yankees,” a source said.