1) A penis, aged to the point where it has absolutely no sexual use.
2) A prick over the age of 50 who does shit just to piss you off.
Woman: Hey there you rich senior citizen, how about coming into the hot tub and fucking me until you have a corinary?
Old Man: I can't, I have an old dick.
or
Jim: That 60 year old guy down the street tipped over my barbeque because he said it was making too much noise.
John: Shit guy, that bastard down the street sure is an old dick.
When oneman grabs the dick of another with a firm grasp and twists his dick.
Man in the background: GRAB HIS DICK AND TWIST IT
Person: Oh my god dude this is a MMA fight Man in the background: THE OLD DICK TWIST Person: YEA!! TWIST HIS DIIIIICK
you know when you wake up in the morning and you havent showered? that smell that your dick has is called day old dick. also can describe how a dicksmells after sex