For young people, I would recommend learning languages they would probably never use in production. APL, Forth, Prolog, Scheme, and one or few variants of Assembly. Unlike modern mainstream languages, these really expand your thinking vocabulary.

And the practical reason why I'd recommend learning these now: you'll never have time to play with them when you're not young anymore. The whole domain of knowledge they represent will forever remain a missed opportunity.

In my book Geometry for Programmers (https://www.manning.com/books/geometry-for-programmers), I also advocate investing in mathematical education and a computer algebra system. Any system. I propose SymPy but it's only because it's free and ridiculously simple to get started with.

The reason for this is also simple. Mathematical knowledge is non-perishable. ChatGPT can write boilerplate for you, and it any language too. But to solve a real-world problem with math, you need a computer algebra system to solve your equations, and your own head to compose these equations. That's something beyond the reach of LLMs.