At 73, how will King Charles face the strain of being monarch?

LONDON — At 73, King Charles III is starting his dream job at an age most men are long retired and relaxing in a comfortable chair — not sitting on a throne.

But the new king has something many of his British subjects don’t have — namely the remarkable genes he inherited from his parents, gerontologists say.

“King Charles has long-living genes," said Dr. June McKoy, a professor of medicine in geriatrics at Northwestern University Feinberg School of Medicine. "Both parents lived a long time. That’s because they have long telomeres, protective caps at the end of a chromosome. Charles could live into his 90s, and the monarchs generally work until they die."

A Northwestern colleague, Dr. Sara Bradley, agreed, noting that Charles' mother, Queen Elizabeth II, was 96 when she died last Thursday, and his father, Prince Philip, was nearly 100 when he died last year.

Both President Joe Biden, 79, and former President Donald Trump, 76, are older than Charles, too.

"Seventy-three is so young," Bradley said. "He had a mother who could work into her older age. Presumably he has good genes and will be around for some time."

That hope was expressed Sunday by many British retirees in the crowd filing past Buckingham Palace to pay their respects to Elizabeth, Britain's longest-serving monarch.

"He's spent his entire life training for this job," said Dave Thompson, 72, of Croydon, a retired auto electrician who was holding the hand of his 3-year-old granddaughter, Ivy Rees. "I'm sure he has his aches and pains like I do. But you just have to get up and carry on, don't you."

Unlike the average Briton, Charles carries the weight of preserving the monarchy — and bearing the praise and criticism that comes with the institution. But he also has numerous people on hand to keep him in top form.

"He's got a lot of support," said Jo Halton, 78, a retired financial consultant who lives in Dorset, south of London.

Not only does Charles have the nation's top doctors keeping tabs on his health, he's got a small army of assistants, aides and household staff helping him get through the day.

"His whole education since the age of 5 has been geared for this moment," said Halton's 79-year-old husband, Les, a retired architect. "He's very fit, very sharp. I think he's more than ready to take over for his mother."

But Charles is also showing his age, said Northwestern's McKoy, who is originally from Manchester, England.

“He keeps fit; he still rides horses and walks on his huge estate," McKoy said in an email. "But there are age-related changes he will not have control over. He has a stooped posture that makes one think he might have osteoporosis. When the bones weaken, people lose some height, usually two inches."

Also, as with many 73-year-olds, "it will take him longer to retrieve information than someone younger than him," McKoy said. "He might try to recall something historical; he knows it’s there, but it’s eluding him."

Rogers Williams is a year older than Charles, lives in Hastings and still works managing a nursing home.

"Yes, I think he's up for the job," Williams said of the new king. "I'm 74 and, in theory, I'm in charge."

"But not of the country," his companion, Wendy Leigh, piped in with a laugh. She is 60 and a retired kitchen and bathroom design consultant.

"But I agree that King Charles is ready to be king," Leigh said. "Seventy-three is not so old anymore."

Asked if he had any advice for the new king, Williams said, "Don't put things off."

"That's what the queen did," he said. "Get it done, you'll sleep easier."

That's excellent advice, McKoy said.

"He will have to be as fastidious as the queen was in having a routine," McKoy said. "The queen always woke up early. Following a routine when you’re older gives the person who is older a sense of cognitive security but also keeps their mood level and keeps them centered. When you have a routine, you don’t get as anxious."

And there's plenty to be anxious about, she said.

“He’s coming into an England that just elected a new prime minister, who has a lot on her plate," McKoy said, referring to Liz Truss. "The country is economically in trouble. The situation with Russia is hard. What the king does is going to be more important than ever because England needs a strong, steady figurehead."

Also, when Shakespeare wrote "uneasy lies the head that wears a crown," he was writing about King Henry IV, who was just 45 when he died in 1413.

“He needs to get enough sleep at night and eat a balanced diet," McKoy said of Charles. "His schedule shouldn’t be too overwhelming. The king might need 30-minute breaks to regenerate cognitively and reset his internal cognitive compass.”

Bradley said Charles was lucky to have his mother as a role model.

"There is research showing your perception of aging influences how you age," Bradley said. "People who have age-positive beliefs age better. People who think you can do a lot when you’re older have less cognitive decline. It applies to him. He has the role model of his mother, a highly active older adult. His perception of being able to do a lot as he gets older is protective for his own cognitive function.”

This article was originally published on NBCNews.com