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.

Wow, I hope it isn't 50!

I think the 50's, 60's and 70's (and beyond) are highly correlated with the challenges we take on.

Children thrive on regular, daily, habitual challenges, mental, social and physical. But so do people in their 90's.

The amount of regression or hard limits on progression associated with aging, that are actually inherent to aging, are surprising small.

Although, reversing long term regressions gets more difficult. And we can run into impediments and unfortunate events beyond of our control at any age, but age makes us more vulnerable.

Firstly, everyone is different and also what worked for one person in their 20's may not work in their 30's. Don't write yourself off, find ways to try out new things and new methods of learning. You can still do lots of cool things.