Malebait
An attractive underage male. Similar to the female version, only not female. For similarities, see "Jailbait" or any of its other forms, but replace female with male, girl with boy/guy, chick with dude, her with him/he, etc.
Cougar-ette (Female in 20s) #1: Oh, wow! That guy is so hot. I want him.
Cougar-ette #2: Oh no way girl! He looks like he's 15 - that's totes malebait!
Cougar-ette #2: Oh no way girl! He looks like he's 15 - that's totes malebait!