Age is taking center stage this election year after President Biden's debate performance at 81 worried even his biggest supporters.

• Why it matters: Americans are living longer — and emerging research offers insight as to why — but not every senior fits the "Golden Bachelor" profile, Axios' Carly Mallenbaum writes.

🖼️ The big picture: The number of Americans who hit triple-digit ages is expected to quadruple over the next three decades.

Reality check: "As much as we want to believe age is just a number, it clearly isn't," Axios' Bill Kole writes in "THE BIG 100: The New World of Super-Aging."

• "We're not the same at 80 as we are at 45," Kole says.
• Brains start shrinking in our 30s and 40s — and much more in our 60s — in the regions responsible for cognitive function.

📖 In his book, Kole highlights what's true for many people who live to 100+.

💍 They have a spouse.

• Married people have a better chance of living to 100 than singles.

💪 They're resilient.

• Super-agers make the best of a stressful situation and move on.

🧠 They have thicker brains.

• Specifically, a thicker cingulate cortex, which is involved in memory and decision-making.
• Worth watching: The proportion of older people with dementia is declining.

🧬 They have a specific gene.

• Half of centenarians have a gene that taps the brakes on height and weight.
• Of note: Smaller animals, like certain dog breeds, live longer than larger ones.

👥 Their siblings become centenarians.

• It's genetics.

🏃🏽 They prioritize exercise and eating well.

• "It's the right combination of both that gives us an advantage," Kole writes.

💬 They're extroverts.

• Most are outgoing, optimistic and easygoing.

👩🏻 They're white women.

• A majority are. Racial inequalities can age people.

💭 Carly's thought bubble: My spritely 93-year-old grandfather, who acts like the mayor of his town, checks several of the super-ager boxes.

• Then again, he also smokes a pipe every weekend.

Go deeper: Kole shares longevity tips from centenarians ... Share this story.

📈 By the numbers: Workers who are 75 and older are the fastest-growing age group in the workforce, according to the Pew Research Center.

• About 9% of Americans 75 and older worked in 2023, compared to 4% who were employed in 1987.

Zoom out: U.S. life expectancy has increased 1.1 years since 2021, to 77.5 years, the CDC reports.