Lionel Richie's daughter -- who turned 21 Saturday -- was greeted with some new wheels on her driveway ... an Aston Martin and a Range Rover. Her boyfriend, Scott Disick, appeared to be responsible for the former, and Sofia made sure to shout him out on IG.

She captioned a vid on her Story, "Wow wow wow Best bf award." When filming her other new car, she wrote ... "New Range. Ok I'm good #21."

Looks like Sofia's birthday celebration was just getting started too -- 'cause shortly after receiving the whips, she drove herself to an airport runway ... where Kylie herself was waiting with a private jet. Seems like them and some friends are off on another adventure.

As you know, Sofia was just with a bunch of the Kardashians on a $250 million megayacht celebrating Kylie's birthday about a week ago on the high seas of Italy, where she and Scott got some QT in on a jet ski. Apparently, KJ and SR are great pals now.

We haven't see the Lord in any of Sofia's videos so far, but ya gotta imagine that wherever she's going now ... he'll be joining the party at some point.