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.

Personally I feel like that conclusion is vague and kinda sucks