Kylie Jenner -- Tyga Takes a Shot at Her ... For 17th Birthday

Rapper Tyga jumped the gun by 4 years Saturday night ... offering Kylie Jenner a shot of tequila for her 17th birthday.

You clearly hear Tyga offering booze to the teen. You can also see Justin Bieber and Kendall Jenner.

They're not in the video ... but The Game and Chris Brown were also on hand.

For what it's worth ... you don't see Kylie drinking. But c'moooon!