The 86-year-old actress has revealed she is hoping to become a centenarian like Captain Tom Moore, who recently raised more than £30 million for the UK's National Health Service amid the coronavirus pandemic by walking 100 lengths of his garden.
Joan explained: "People make too much fuss about age, which is just a number. I think there's a big difference between biological age and the age you're supposed to be."
The actress insisted she applies the same attitude to her marriage.
Joan - who has been married to 55-year-old Percy Gibson since 2002 - jokingly told the Daily Mirror newspaper: "As you know, he is somewhat younger than me. At first people would always say, 'What are you going to do about the age difference?'
"I'd say, 'Well, if he dies he dies.'"
Joan also admitted to being inspired by 103-year-old actress Olivia de Havilland.
She said: "Will I outlive you all? No, I don't want that.
"I'll settle for 100 years old, like Olivia de Havilland, who played Melanie in 'Gone With The Wind'. She lives in Paris and is still going strong."
Meanwhile, Joan recently admitted she's refused to watch the news during the coronavirus lockdown because she finds it "too depressing".
The London-born star shared: "Hand in hand with physical health comes mental well-being. I'll usually have the TV on but not the news. It's too depressing.
"Percy and I have a rule that we'll watch in the morning and catch up at 6pm. We might watch a movie, but it would be too easy to sit in front of the TV, so after work, Percy and I try to play a board game instead - usually Scrabble or gin rummy."