Arnold Schwarzenegger is being made to feel old by his granddaughter.

Arnold Schwarzenegger

Arnold Schwarzenegger

The 73-year-old actor is relishing the challenge of helping to raise eight-month-old Lyla - the daughter of Katherine Schwarzenegger and actor Chris Pratt - but he admits that she's making him feel his age.

The former governor of California said on 'Jimmy Kimmel Live!': "The only thing is, it makes me feel old to think about, 'Now I have a grandchild'. But it's really great having a grandchild.

"It's a beautiful, beautiful baby - baby Lyla - and I'm very proud of Katherine and Chris. They're doing really great together as parents."

Arnold admitted he had a much more hands-on role with his own children, revealing his daughter is now an "expert gatekeeper".

The Hollywood icon - who also has Joseph, 23, Christopher, 23, Patrick, 27, and Christina, 29 - shared: "When my kids were growing up, I participated, and it was a lot of fun to do that. But I have never changed diapers on Lyla, because I think that Katherine is the expert gatekeeper. She just, whenever you touch the baby, says, 'Oh, my god! Oh, my god! Like this.'

"I said, 'Katherine, come on, now. I've held enough children in my hands. I know exactly what I'm doing. I'm an expert in that stuff.' She just freaks out and does it. [But] I think it's natural."

During the interview, Arnold was also asked for his opinion of Caitlyn Jenner's decision to run to become the governor of California.

He said: "The key thing about all of this is, it doesn't matter if it's Caitlyn or it's anyone else. Do you have a clear vision where you want to go? What are the kind of changes you want to make, and why are you qualified to become governor?

"That's what you have to convince the people."