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1.
When someone who isn't a teenager displays the traits often associated with emo
My dad is so oldmo, perhaps I should hide the razorblades...
by bluehouse June 09, 2006
 
2.
Basically the opposite of a chimo. A teenager or someone in their early twenties that can not get enough of middle-aged or older men.
Cassandra: Dude, Shane is sooo hot. With a million o's.

Amber: Dude, he's like 34...

Cassandra: Do you think I care?

Amber: Dude, you're the biggest oldmo I know.
by Cassandra Q February 26, 2010