N.O.D or NOD
acronym for Narly Old Dude or Narley Old Dude, the guy over 40 still mixing it up with the 20-something's, the one with the mountian bike, surfboard, skateboard, guitar, he's running, he's in the gym, still competitive in nature, and probably dating your girlfriend.
Hey, anybody can do this in their twenties, but that guy's a NOD.