Looking good, Alex Rodriguez! The athlete, 48, flaunted his fit physique via Instagram on Thursday, January 4 — just a few months after he revealed he lost over 30 pounds due to the help of his girlfriend, Jac Cordeiro. In a new photo, the Yankees star showed off his abs alongside the blonde beauty as they posed for a mirror selfie on vacation. Rodriguez also posted a video of himself driving around the Dominican Republic with no shirt on, while Cordeiro, who also trains Rodriguez’s ex-wife, Cynthia Scurtis, wore a sports bra and biker shorts. In September, the baseball legend shared how excit…