A phase during adulthood when a man first develops moobs. Usually begins in mid to late 30s but has been known to happen in late 20s in some male office workers.
Larry: Holy crap Frank, I didn't know you'd reached mooberty already, your moobs are huge!
Frank: yeah it sucks, I've started getting moobsweat too. I wish my mother would buy me my first man bra.
The only way to explain the meaning of the word Mebert, is in the Mebert language, which consists only of the word Mebert, said in various pitches, volumes, and inflections.