Scott Disick Finally Growing Up With His Teen Girlfriend, Sofia Richie (Details, pics)

All Scott Disick needed to settle down and lay off the nightclub scene was the love of teenage but yet very mature, Sofia Richie.

Sources connected to the couple tell TMZ... Scott's backed off his hard partying ways since he and 19-year-old Sofia started hanging out romantically a couple months ago. We're told 34-year-old Scott feels her age isn't an issue, because she's used to the spotlight after growing up with her actor father, Lionel Richie.

Although they've traveled to a lot of countries in a short time -- Milan, Miami and Mexico -- they've been laying low wherever they go, hanging mostly in restaurants and beach instead of clubs.

Scott is also aware of the change, telling friends ... Sofia's "been really good for me." And let's face it, this relationship's going way smoother than his previous with a 19-year-old -- no offense to Bella Thorne.

As for his other ex? Scott's accepted Kourtney Kardashian's moved on, and we're told he's happy to be doing the same.