Basically, when referring to people, it takes the standard adjective, and uses it as a noun instead.
The Olds want their medicare and SSI, but they hate sushulizm.
I was T-boned at the intersection by an Old who ran the red light.
Person 2: "Well you see, my Dad just got diagnosed with O.L.D."
Person 1:"O.L.D.? Oh im so sorry, I hope he gets better."
Person 1:"Wait, whats O.L.D.?"
Person 2:"Hes old, that's all."
Annabelle: Don't blame him. He's just old.
Sarah: I'm only 22. I wasn't even born when the Vietnam War was going on!
Annabelle: He's not just old, he's OLD.