Henry Winkler has credited "good genes" and the "will to be young" with not feeling his age.

The 'Happy Days' actor - who is best known for his role as Arthur 'The Fonz' Fonzarelli in the iconic sitcom between 1974 and 1984 - celebrated his 78th birthday on Monday (30.10.23) and he's refusing to consider retirement.

He told 'Entertainment Tonight': "I have good genes! [And] just the will to be young.

"You know, people say, 'Are you gonna retire?' I don't even know how to say the word. Working is in my DNA."

Physically, Henry is feeling "great" too, and he's glad to still have a career, having most recently lent his voice to shows like 'The Legend of Vox Machina' and 'Wolfboy and the Everything Factory', while he also had a cameo as Uncle Al Pratt in 2022's 'Black Adam'.

He added: "Well, aside from my knees, I feel great! I really do. I'm here, I'm doing it, I'm still being a part of the world.

"It is just amazing, truly, because there are so many people who are my age who feel old, who feel forgotten."

The actor - who has also released his new memoir 'Being Henry: The Fonz... And Beyond' this week - is glad to have projects to keep himself mentally "agile".

He explained: "Being an actor or writing, it so keeps your mind agile.

"Acting is like putting a jigsaw puzzle together in order to create a human life, and writing a memoir, you have got to really remember not only what you think you remember but the events around it."

Meanwhile, he also addressed his reputation as being "the nicest guy in Hollywood", but insisted it's more to do with being "happy" with life.

He said: "You know, people always say I'm 'the nicest guy in Hollywood.' I'm not nice so much as I am joyous.

"I am happy to be on this Earth, to meet the people I meet, to meet the people in this building, coming to this studio."