Lil Wayne Celebrates 40th Bday with YG, Keith Sweat, Skip Bayless

Lil Wayne got an early start to his 40th birthday celebration ... with a star-studded birthday party fit for the legendary rapper!!!

Sources close to Weezy tell TMZ Hip Hop ... the shindig went down at popular L.A. hot spot, The Nice Guy -- and several close friends and family members -- including all 4 of his children, flew in from New Orleans for the event.

Special guests ranged from YG and Yella Beezy to Mack Maine and Cortez Bryant on the hip hop side ... and Skip Bayless, Shannon Sharpe and Marcus Wiley repped for the sports culture.

NBA YoungBoy understandably couldn't be there on an account of his highly publicized house arrest, but sent a video message addressing Wayne as "his son" ... as they're both branches from the Louisiana rap family tree.

The biggest shocker of the night came courtesy of R&B legend Keith Sweat ... who surprised Wayne with a special performance of his classic track "Don't Stop Your Love."

Wayne's actual birthday is Tuesday, when he'll be getting the royal birthday treatment from the National Museum of African American Music in Nashville. We've learned they're unveiling a special exhibit in his honor.

NMAAM and Vanderbilt professors will host an event for the exhibit, which features personally donated antiques from Wayne -- including his Best Rap Album Grammy for "Tha Carter III," his first handwritten letter during his stint on Rikers Island and much more.