Yeah there are quite a few exceptions to this. I've been (re-)reading The Making of the Atomic Bomb, and two of the four people directly involved in the discovery and explanation of nuclear fission were 60 (Hahn and Meitner) the other two (Frisch and Strassman) were in their mid-to-late 30s. Shortly after, Bohr (53) figured out that the oddities of uranium's fission behavior were due to the different activation energies of U-235 and U-238.

I think the best place to look for major works late in life is probably historical writing, which calls for accumulated knowledge and wisdom. Looking at the four most recent winners of the Pulitzer Prize in history from 2023-2025 [0], all appear to be north of 50 based on their Wikipedia pages (which give dates of education if not dates of birth), and one is in her 70s [1].

[0]: https://en.wikipedia.org/wiki/Pulitzer_Prize_for_History [1]: https://en.wikipedia.org/wiki/Jacqueline_Jones