Now, the major candidates on both sides are in their 60s — except for Ted Cruz and Marco Rubio, who are 44, and Bernie Sanders, who is 74. Donald Trump is older than Hillary Clinton, although of course when we talk about the possibility of a Trump presidency, age is about the 4,353rd topic of concern.

It’s not that age no longer matters, but that we’ve come to realize it hits different people in different ways. Some lose energy and focus, while others seem to get smarter and stronger. Justice Ruth Bader Ginsburg of the Supreme Court, at 82, does push-up routines with her trainer. Gloria Steinem celebrated her 80th birthday riding an elephant in Botswana.

In high-end politics, what we need to know is less about calendar years than staying power. Marco Rubio keeps talking about “generational change,” but he seems to have less energy than a koala. (Koalas sleep 18-22 hours a day. I am bringing this up so you can’t say I never teach you anything.) Really, where is that man? He hardly seems to be campaigning and he misses nearly half the Senate votes. Pre-millennials, is this the guy you want representing you?

Meanwhile, Clinton wowed the country with her endurance during this week’s Benghazi hearing. If we remember the House Select Committee on Benghazi at all, it will be as the folks who gave Hillary a chance to demonstrate her staying power. Even accounting for breaks, 11 hours of questioning must be close to some kind of record.

“Yoga always helps,” Clinton said as she departed.

She is — except for the part about yoga — a throwback to the first era of American public women, people like Elizabeth Cady Stanton and Susan B. Anthony, who came into their own in late middle age. Stanton, who like Clinton had an ability to make herself nap at will, kept promising the impatient Anthony that when her kids grew old enough to fend for themselves it would be exactly the right time for their great campaign for equal rights. “We shall not be in our prime before fifty, and after that, we shall be good for twenty years at least,” she assured Anthony. Actually, both of them were good for quite a bit longer, and still giving speeches at 80. Justice Ginsburg has a picture of Stanton in her Supreme Court office.

Clinton will be having a birthday party on Sunday in New York, and naturally it will be a fund-raiser. That sounds like the worst possible way to celebrate, but if there’s anything we know at this point, it’s that she can take the stress.