VIDEO: Justin Bieber- I wanted to bang Selena since I was 15 years old

Justin Bieber hatched his plan to nail Selena Gomez 2 years before they dated -- while she was still dating a Jonas brother -- and TMZ has the footage that proves it.

A 15-year-old Bieber confessed the scheme back in July 2009 -- during an interview with L.A. radio host DJ Skee that was lost in oblivion -- saying his celebrity crush was Selena Gomez ... who was dating Joe Jonas at the time.Bieber immediately blushes like a schoolgirl and says, "Nobody heard that" -- but less than two years later he attended a Vanity Fair Oscar party with the girl of his dreams...see video after cut ..