Difference between 大兄弟 and 小伙子 Difference between 大兄弟 and 小伙子.

Under which condition should we use one of them?
小伙子 is young guy. It's a generic term to address a young man. 

大兄弟 is used in north, which sounds pretty folksy. It's used to address a man and is said by some older people. Sometimes, we make a joke to address a guy as 大兄弟.