Raul Rosas Jr. is ready to find out how much he has grown.

The 21-year-old bantamweight returns Saturday at UFC Vegas 121, where he will headline the event against veteran Raoni Barcelos in the first five-round main event of his UFC career.

Rosas Jr. enters the matchup riding a five-fight winning streak, most recently earning a decision victory over Rob Font at UFC 326 in March. Although he wanted to find a finish, Rosas Jr. believes the difficult fight gave him valuable experience at the highest level.

“I would have liked to finish, but it helped me improve. It helps me improve. I'm doing it at a big stage where I'm young and I'm having to adjust and learn from these fights at a big stage, so I'm proud of myself to be able to be doing it at this level,” Rosas Jr. told UFC News.

The young contender dominated large portions of the fight with his grappling but acknowledged that controlling an experienced opponent like Font for three rounds was no easy task.

“Obviously I would have liked a better outcome, but I'm still happy with how I was able to do it, able to handle Rob Font which is not (easy). Yeah, I grappled him for three rounds but it's not easy to do that, you know? So I'm proud of myself.”

Now, Rosas Jr. faces another major challenge in Barcelos, who brings nearly two decades of professional experience into the matchup.

The 39-year-old Brazilian is also riding a five-fight winning streak, making Saturday's main event a particularly intriguing test for Rosas Jr. as he attempts to establish himself among the UFC's top bantamweights.

For Rosas Jr., however, the five-round format is just as exciting as the opponent standing across from him.

“It's different managing a five-round fight for sure and I'm excited to go in there for the first time for five rounds,” he said.

“It makes me more excited if it does go to fourth and fifth round because I'm starting to get used to this as the championship fights are coming.”

Rosas Jr. knows he will have to deal with an opponent who has considerably more experience, but rather than viewing that as a concern, he sees it as an opportunity to discover another level of his game.

“He's a very tough opponent, a very experienced guy to be honest. I think he's the toughest opponent I've faced so far, and that's what makes it exciting for me because I'm willing to go out there and figure it out,” Rosas Jr. said.

“So I think he's going to bring new things out of me and a best version out of me. So I'm excited to see what happens Saturday night.”