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1.
To have a love interest that is significantly younger than oneself in age.

antonym=rob the grave
Typically, older man and younger women, but not always.
"I want to rob the cradle, I want to trade my 40 year old wife in for two twenty year olds"
For example, further than 5 years apart in age might signal a cradle-robbing". Even more years yells it!
by kiddm April 28, 2007
 
2.
to date a girl thats much younger than you, or thats just plain young(say 14 or younger)
"Man, jimmy's girlfriend is 13, hes robbin' the cradle!"
by cody July 01, 2003