I think the phrase is "kickin' it old school". It means "doing things the way we used to in the past". For instance, beat boxing (doing rhythms with your mouth only) started a while ago. If a bunch of guys get together and start beat boxing in the original style from when it first started, they'd say they were "kickin' it old school". In this video, the boy meant something like, "We are hanging out on the rooftop the way we used to when we were just kids." It's just a joke, obviously, since the kid is ... just a kid himself! ... and he had never hung out on rooftops with 50 Cent before now.

haha, man what are you doing here, it's private :D damn, i can't delete it. haha

hahaha kicking it old school. Just ask Qwarik :D