Frank Kelly does not want to talk about old age, but it is a subject he cannot avoid. As Father Jack Hackett in Father Ted, he was one of television’s best known hilarious old men. Now he’s in Scotland to play the title role in My Old Man, a play about a former cruise-ship entertainer who wakes up in hospital to discover he is no longer as young as he once was.

“I have never thought about old age until I was bombarded with questions about it over the last year,” says Kelly, who recently refused to contribute to an Irish television programme about the process of ageing.

“I wouldn’t do it as an actor because it puts you on a museum shelf. If people get it fixed in their mind that you’re 66, they won’t get you to play a 53-year-old.”

Although he is a father of seven, not to mention a grandfather of 12, Kelly has always lived in the moment and sees no reason to slow down merely because he has passed the usual retirement age.

He looks in rude health as he hunches over a cappuccino in Glasgow’s Tron theatre bar. Like Father Jack, he has a ruddy pallor, but his is the healthy glow of a keen hill-walker, not the dipsomaniac crimson of the alcoholic priest.

“Disability will come when it comes,” he says. “But I have always attended gyms and I swim in the winter in the sea, so I’m unreasonably fit for my age. My father was a much older man at my age. I suppose all this fitness and training is a whistle in the dark; it’s an attempt to stay alive for ever. But I don’t analyse it, I just like feeling well.”

He’s taller than the foul-mouthed Jack seemed — and a good deal more eloquent, as you would expect for a man who trained as a lawyer. He was only in his mid-fifties when the three series of Father Ted were filmed, which explains why the first make-up session took 2½ hours.

“I don’t think it was immediately apparent to anyone that Father Ted was going to be a success,” he says. “What I was doing was so minimalist it was alarming. But I knew when we went into the studio and all the outside footage we’d done in Co Clare was shown on a big screen. When the studio audience fell down laughing, I knew it was a winner. That made it a joy to do the studio material.

“Father Jack was modelled on a character I’d done on television before. Minimalist acting takes a lot of concentration because you’ve got to score when you score. I call it ‘numb-buttock acting’ because you find yourself in an uncomfortable position and you know that the shot has been framed, so you can’t get off that buttock until the end of the shot.”

The rubber body suit underneath his cassock could not have made things any easier.

He puts the show’s success down to the brilliance of the performances by the late Dermot Morgan, Ardal O’Hanlon and Pauline McLynn as well as the multilayered quality of the scripts by Graham Linehan and Arthur Mathews. “It is the Beano comic; the bomb has ‘bomb’ written on it; it’s send-ups of movies and it’s satire,” he says.

To those who question the stupidity of O’Hanlon’s Father Dougal — which is, of course, the joke — Kelly points out that every workplace has an employee whose qualifications are a mystery to his colleagues.

His own character is arguably even closer to the reality of the modern clergy. “Father Jack is not such an uncommon phenomenon,” says Kelly, himself a Catholic. “A number of priests have said to me that they have one just like him. With the gap in recruitment to the clergy, you do find religious orders where old men are looking after very old men who have lost the plot. And the priesthood is something you don’t retire from.”

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