André 3000 Says Age Affected His Ability To Rap In OutKast

André 3000 is coming clean about his decision to walk away from OutKast at the peak of their success ... saying he simply lost his drive to rap.

In a video interview with GQ to promote his upcoming instrumental album, André not only admitted his creative juices for the group had dried up but said he hasn't been harboring a boatload of unreleased raps like everyone accuses him of.

At 48 years old, 3 Stacks says sometimes rapping even feels "inauthentic" for him ... and he feels like he'd have to make more age-appropriate music -- in his case, dropping bars about having a colonoscopy and trips to the eye doctor.

OutKast's 2004 album "Speakerboxxx/The Love Below" was certified 13x Platinum this year -- making it the biggest-selling rap album of all-time ... but as Sleepy Brown hinted to us in the summer, André was embarking on another journey ... one without words.

The new project "New Blue Sun" is mainly composed of his flute recordings ... the opening track is titled "I Really Wanted To Make A 'Rap' Album But This Is Literally The Way The Wind Blew Me This Time" --- and there's even a warning label informing fans there are no bars to be found!!!

André tells GQ that his chemistry with Big Boi changed over time and while he didn't want to be thrust into the limelight again, he needed the press run to promote the music he believes in so much.