I see your point, but the examples I notice across fields including writing, demonstrate a strong preference towards [relative] youth.
- Neal Stephenson (My favorite fiction writer) published his first book in his early 30s
- Hemingway published great works in his early 20s
- Almost all of the most notable scientific breakthroughs in the 20th century were from individuals in their 20s. Schrodinger was the Old Man at 37!
- Most famous musicans started releasing their first, and often best, albums in their early 20s-early 30s. When they tour into old age, they're mostly playing their hits of youth.
I think, perhaps, the trend is even more pronounced in scientists than writers. Skews early-20s.
You can find exceptions, but the exceptions are often not that old, and in the anecdotes I think of (Favorite authors, writers, musicians etc), it's hard not to notice the trend of youth. I want to find this trend to be untrue because it can be depressing, but can't. (This is at the core of the article)
Possibly you could look at Newton's example. Yes, his best scientific contributions happen when he was young, and they are what he is known for. But in his late 40's he gave that away. Perhaps as you say it got too hard.
Instead he took up a job at the mint. The job had some technical bits to it like designing coins that were harder to counterfeit, but is was mostly a managing people and society job. The coin clippers were literally debasing the currency to near worthlessness. Had they continued they would have been the internal cancer that took down the empire, as the state could no longer afford to pay for the ships and men needed to create and maintain it. Newton almost single handedly turned that around. It's not an exaggeration to say he saved the empire.
You say the older Newton could not do what the younger Newton did, and that's probably true. But it's also true the younger Newton could not have done what the older one did. He needed the experience and understanding of how men and society work that only decades of live could give him. So yes some abilities dim as you age. But other abilities grow stronger.
I don't think it's reasonable to include (pop) musicians. Pop music fans, who decide what's a hit, skew young, and are influenced partly by how much the star prancing on stage attracts them as an imaginary sexual partner (or role model). Stardom involves a lot of intuition, charisma, and personality, all things a young person might have by accident. There's also a "voice of the [...] generation" trope that's more plausible if you are one of that generation. So yes, many albums are released by youthful stars and gain attention due to their youthful relevance, sex appeal, and physical fitness (non-rusty voices, nimble fingers, jumping about): and if coincidentally also good music, they're likely to overshadow later albums that are only good music but connect with less visceral urgency to their audience. With, as you say, many exceptions (Wilburys).
It is quite interesting to compare these ages to all the people you know.
There are probably roughly zero 20-somethings that are more interesting than the most boring 50-year old you know.
Is it maybe the case that 20-somethings have nothing to do so they futz around with science and writing and can do that. As they grow older they find better things to do?
You can find exceptions, but the exceptions are often not that old, and in the anecdotes I think of (Favorite authors, writers, musicians etc), it's hard not to notice the trend of youth. I want to find this trend to be untrue because it can be depressing, but can't. (This is at the core of the article)