Someone who persists at an activity, like sport, despite hardship and age, maybe when they should have retired or given up a long time ago.
Dean McDonald is such a warhorse on the footy field. He's always injured and broken down but does his best to get back into the game.
A term referring to an old, retired military man.
"I'm not a colonel anymore...I'm just a retired ol' warhorse."
-Colonel Campbell, MGS