Russian secret agent Illya Kuryakin's famous blonde fringe may now be streaked with grey but McCallum's not counting the years.
He still signs Illya Kuryakin autographs for fans who stop him in the street -- even though the last UNCLE episode was three decades ago.
He said: "To some people I'll always be Illya Kuryakin and I don't mind -- that Russian spy was very good to me!"
McCallum will celebrate his 65th birthday in September by cycling 270 miles from Boston to New York to raise funds for charity, and his workload is as heavy as ever.
Last night at the luxurious New York flat he shares with his interior designer wife Katherine, 54, he said: "Retirement is an obscene word. I don't feel any different inside and the beauty of growing old is that your wife, family and friends all grow old with you -- so it all helps.
"And I'm working as much as ever. I'm just an old hustler. I do TV, radio, voice-overs, theatre -- I'm always very very busy and I don't have the time to grow old."
But he does admit to giving in to one elderly privilege -- and hoots with laughter at his own brass neck.
He said: "I often go into Denny's or one of the wonderful coffee shops here in New York for a 'senior discount breakfast' which consists of one egg, one rasher of bacon, one sausage, one slice of toast and a cup of coffee for a very cheap price. It's wonderful because it's all you really need. At this age you don't need these vast breakfasts.
"And I also get cheap tickets to the cinema because the age of the senior citizen here starts at 62."
He said: "We filmed in Cornwall and my character, Major Billy Fawcett, isn't a nice chap at all.
"He seduces a young girl, shatters her innocence and has a profound effect on her future and the way she sees men. He's really quite ghastly but it was great fun."
McCallum will also be coming home in June when he returns to his Scottish roots for a short break with his family in Stirlingshire.
He said: "I have many happy memories of my Scottish childhood. My father was Sir Thomas Beecham's concert violinist and leader of the Scottish Symphony Orchestra and we moved from Scotland to London when I was three." When war broke out, young David went to stay with mother's sister Margaret in Stirling.
He said: "Then my mother joined us and we took a little cottage in Gartocharn near Loch Lomond.
"I think I dammed up every river and burn in the area. I must have been a nightmare to farmers. For a young boy, it was a great adventure.
"And of course even when we moved back down to London I spent all my summer holidays in Stirling with my Aunties Kitty and Margaret, and my Uncle John.
"Now they're all elderly. Kitty and Margaret live in Bridge of Allan but Uncle John is now in a wheelchair and has up residence in Bannockburn Hospital so I'm desperate to get over to Scotland to see him, and hope to be there within the next ten weeks."
McCallum moved to New York in 1968 after his marriage to cancer victim Jill Ireland ended in divorce.
He's been married to Katherine Carpenter for 23 years and reckons New York is one of the best places in the world.
He said: "I don't ever see us coming back to Scotland. New York is wonderful. We've got a great mayor and the crime rate is coming down all the time.
"I think home is where your family and friends are. All my children are in America, and this where Katherine and I have built our lives.
"Our son Peter is now 27, our daughter Sophie is 24, and now moving back home again from university.
"My sons from my first marriage, Val, 34, and Paul, 40, also have their lives here. Val's a musician who has just started a new show with Sheryl Crow, and Paul's a writer."
He's also a grandfather. His son Jason -- during his his marriage to Jill -- died of a drink and drugs overdose seven years ago and left a two-year old son, Tory.
David said: "Tory's now nine and lives in California with his mum. We don't get to see each other that often, but we keep in touch and I send him presents and stuff."
He admits he still gets a kick out of being recognised from his many TV roles, including Illya Kuryakin in The Man From UNCLE, Diana Rigg's ex-husband in the award-winning Mother Love, Steel in Sapphire and Steel, The Invisible Man, and Trainor.
He said "I think I'm very lucky to have lead such a wonderful life. But I've no intentions of slowing down just yet."