Attributing "young man's game" to G. H. Hardy, he'd had a heart attack the year before he published A Mathematician's Apology, and by all accounts, had lost much of his drive and energy.
The whole book has something of a sad tone to it.
The whole book has something of a sad tone to it.
I rather dislike it, and am glad Einstein was wrong about various things (:
So he may have been projecting his own disappointment into a general statement.
For example, The Abel Prize [1] does interviews with their award winners every year and quite often they are asked about this question, and most of them agree that as a mathematician your peak "mathematical powers" so to speak and energy are at their highest in your 20s and 30s, while afterwards you have to rely more on experience to make up for it as you grow older.
Remove your limits and you'll be as productive (if not more productive) than any 20-something, though you'll probably do stupid things from time-to-time. Don't be afraid of being stupid, after all, it has no bounds... :p
In all seriousness though, just spend an afternoon coding something you wouldn't normally code without thinking about it first. As you get older, it's harder to just cowboy code something without stopping to think about it. With some practice, you can bang out some pretty high quality code very quickly. And then you'll eventually learn when to cowboy it and when to think.
My 2¢. YMMV.
>This isn't exactly what you were asking for, but Littlewood himself, after overcoming depression at age 72, did good mathematics throughout his 80's--it's hardly a young man's game.
(Littlewood is Hardy's pen name)
Littlewood was reported to be quite amused when he heard this.
And of course the story might be apocryphal. Especially since it's also attributed to Edmund Landau and Norbert Wiener.