Reality TV star Kylie Jenner is still a teenager and is dating 25-year-old rapper Tyga, partying and jetting around the world without any supervision. And her father Bruce Jenner is concerned.

According to a source, the former American athlete is not liking the way his daughters Kylie, 17, and Kendall, 19, are dating older men, reports radaronline.com.

`For the longest time, Bruce kept the divorce amicable. But now that it's finalised, he's ready to stop stepping back,` OK! Magazine quoted a source as saying.

`It's killing him to watch her look the other way as (Kylie and her sister Kendall) date older guys and make one bad decision after another,` the source added.

Though Bruce, who is now divorced from Kylie's mother Kris Jenner, doesn't have much say in what Kendall does, rumours of Kylie's drinking and wild partying have him concerned, and a video that surfaced showing her partying with Tyga, Justin Bieber and The Game on her 17th birthday only compounded his fears.