over the course of their career this means that they are slowly falling behind as they have less time to gain the experience that men are getting.
I've seen this theory, often pitched by the same people who argue for The "rational marker hypothesis" in the face of all evidence that humans are irrational beings prone to fantasy and panic.
Human beings also don't level up in skill in a linear manner. Beyond a couple of years, ability (and willingness to learn) far exceed tenure as markers of competency. I'll take an eager mother of 3 over a coasting single man 100/100 times. He might be in the office all weekend, but the mom is going to get stuff done (or ask questions) because she ain't got time to dick around.
But here's the rub: the job market isn't any more rational than the stock market. Mere tenure (or a degree) are easy to prove, and as such are held up as key qualifications. So those types of people get the jobs and tenure in those jobs qualify those people for even better jobs.
Meanwhile, taking a break from the workforce to raise your kids sends you back to retail hell when you try to come back, because your advanced degree and years of experience suddenly doesn't count for anything because apparently the whole world changes over 3 years.
It's not explicitly sexist. Most people don't actively discriminate. It's just a bunch easy, lazy or arbitrary decisions that pile on top of each other into vicious and virtuous cycles. Hanlon's Razor carves systematic sexism.
Who cares about the age or experience difference? It's the same role, so why shouldn't she receive the same pay? Did the role suddenly become less difficult or less time consuming after Capaldi left?
Difficulty is irrelevant. Salaries are like any other negotiable good: the price is always what the market will bear, and what the market bears depends on the number of options available. If Capaldi has more options than Whitaker, he can leverage that into a higher salary and vice versa.
TBH, I can't give a shit about whether or not Celebrity A gets paid more than Celebrity B. No matter who wins it doesn't change the greater labor market, which is where the problem is, not to mention my own interest. I get more leverage to earn more when the guy greeting me at Walmart does, not when a millionaire gets more millions. Holding all else equal, at least.