Oldtarded
Doing really dumb things when you're old enough to know better, but not senile enough to have an excuse.
“Grandpa parked the car halfway on the lawn again. Is he getting old?”
“No, he's only 60. He just doesn't care if he's lame. He's being oldtarded.”
“No, he's only 60. He just doesn't care if he's lame. He's being oldtarded.”