Colin Farrell has joked his "hips don't lie" as he approaches his 50th birthday

He told Extra: "5-0, half a century, man! I mean, my hips feel like it... Hips don't lie. Hips, knees, all that good stuff.

"My spirit doesn't feel, I don't know what a 50 year old spirit should feel like... I have no idea."

Colin insisted he's got no big plans to celebrate five decades of life, besides potentially a quiet few days in the great outdoors.

He added: "I'm not going to do anything. Very little. Very little.

"I might take myself away to a motel for a few days and go on a couple of jogs."

Colin - who has sons James, 21, and Henry, 15, from previous relationships - plays an addict in his recent movie Ballad of a Small Player and he explained he's drawn to roles exploring the dark side of life, because all humans experience bad times.

Speaking to Jessie Buckley for Variety's Actors on Actors series, he said: "I have mad moments of joy in my life and joy in work and joy with my kids.

"But I've always felt that the common denominator in regard to experience as humans is pain.

"The one thing we've all felt, really, is pain. I put fear and uncertainty under that banner.

"Not everyone, sadly, has felt joy. And that's a great tragedy.

"But I'm fascinated with pain. Every single act of aggression or violence has its root in pain that has become personalised."

Colin - whose eldest son has Angelman syndrome, a rare genetic disorder - knows his work is a "privilege" in the way it allows him to explore all his experiences and feelings, but he is also aware that it can't change his life in a significant way.

He said: "The permission to be overwhelmed is a huge thing to give to each other, to give to our kids.

"I'm so f****** aware of the amount of privilege that I've experienced in my life and what rare air I fly in regarding what I do for a living. But at the end of the f****** day, there's nothing I can do in acting that can make James, my oldest boy, talk or have language."