Los Angeles, March 27 (IANS) Actor Paul Rudd has quipped that his secret to staying youthful is having "darkness" in his heart. He says he is actually "80 on the inside".

Asked by people.com at the Chicago Comic and Entertainment Expo (C2E2), what keeps him so youthful, he said: "I'm 80 years old on the inside."

He then pointed to his chest and joked: "In here, pure darkness. And a little moisturiser."

Although the "Avengers: Endgame" actor looks youthful, he said last year that he used to constantly worry about having a mid-life crisis, and said he has been pondering life's big questions since he was in his 20s.

He said: "I think that one of the great joys in life is knowing that everything's ahead of you -- the big questions, such as: 'I wonder what I'm going to do for a job when I grow up'; 'I wonder who I'm going to marry'; 'I wonder if I'll have kids'; I wonder what their names will be'; I wonder where I'm going to live'.

"When I was younger, if everything got me down it didn't matter because all that was ahead. I think that it's sometimes harder in life when those questions have been answered and all of a sudden you think, 'what do I have to look forward to?'

"In my 1920s I often thought I was casually strolling towards a mid-life crisis, and it started picking up speed all throughout my late 20s, 30s, 40s ... I joke, but then there's truth in that."

The 'Clueless' star said he is still trying to work out how not to be a "d**khead", while also balancing his ambition to be a normal dad with his movie-star status.