I want this to be true, but I do not know who this Aaron guy is and I do not have the time or skills to check the sources. Not sure what to do about that. Wait and see if this is something I see bubble up as some kind of accepted thing among scientists involved in those kinds of studies?

Here's what Perplexity Pro deep research has to say about it (pasting only the conclusion for brevity):

The article's claim that cognitive ability peaks between ages 50-60 contains elements of truth but is misleading in its breadth and certainty. While longitudinal research does show that cognitive decline is less severe and starts later than cross-sectional studies suggested, the evidence does not support a simple peak in the 50-60 range for overall cognitive ability.

Key takeaways:

Crystallized intelligence may continue improving into the 50s and 60s

Different cognitive abilities peak at different ages

Individual variation is enormous

Methodological issues in both cross-sectional and longitudinal studies complicate interpretation

The 50-60 "peak" claim oversimplifies a complex, multifaceted process

Rather than a single peak age range, the evidence supports a differentiated model of cognitive aging where various abilities follow distinct trajectories, with substantial individual differences influenced by health, education, lifestyle, and genetic factors.