I'd say C is actually a pretty good choice for an educational project like this. Having to write out all of your data structures by hand and manage your memory manually is a good learning experience, and since you're not writing serious production code, you don't have to worry too much about making mistakes.

Given OP's (presumed) age, curiosity and enthusiasm, my advice to OP would be to not worry about what language you are going to specialize in at all. That can come later. In fact, do the opposite: learn every language under the sun and prioritize weird languages with unique ideas that are outside of the mainstream. Learn Rust, Haskell, Lisp (OP is already learning Racket so that's covered), Prolog, Forth, assembly, Smalltalk, ... (admittedly I haven't learned every language on this list; there are some that I wished I learned when I had more time for it).

OP is at a stage in life where fluid intelligence is still very high and crystallized intelligence is growing rapidly. This is the time in your life where you are perhaps most able to absorb new ideas and ways of thinking, before you get set in your ways and less receptive to different ways of thinking.

C is a very popular language to use in undergrad courses, all our entry classes (intro to programming, data structures and algorithms, OS fundamentals, etc.) were in pure C - exactly because you have to deal with memory from the get-go.

If that's the case at the Uni OP is studying at, then he should be come fluent in C - because from experience as a TA, it's not necessarily the CS knowledge/fundamentals that tend to be lacking when people struggle with classes, but rather that they're fighting a new language. Even if they have years of previous experience...especially in these days, when Python or JS tend to be the first (and only) language to many freshmen.

This is bad advice.

> several better options these days

Every other option requires you to buy into some additional paradigm-of-the-day.

You can easily lose decades going down the wrong programming rabbit holes.

They built an interpreted language in C over a summer, I think they are beyond “getting into programming” - they’ve clearly been programming for years.

This kid has plenty of time to dive into other languages. C is a great choice.

C is like a high level assembly language. It maps very closely to how the computer actually runs programs. That, and it’s simplicity, make it a great way to learn.

It’s not usually a great idea for production code anymore, but for learning it’s fantastic.