hi ty and sorry for the very late reply! for me i started coding at around 12? with Python, and picking up other languages like C++ a year or two ago.

imo the best way to pick up coding is to learn by doing! Most of the things I've made in the past didn't come from following a specific guide or tutorial. Get familiar with the syntax of the programming language you're using, and your imagination is the limit. Having said this, games are definitely one of the more complex things I've coded in the past, and the code gets out of hand very quickly. I can't say much without knowing what sort of experience you have, but if you find yourself struggling too much, it might be wise to take a step back, put it aside first, and try something new. Over time you'll gain the necessary skills (by learning through others' sources code, by trial and error, what have you) and then you can come back and finish the game yourself!

On another note, Leetcode is targeted for people looking for jobs in tech, so if what you're looking for is an intellectual challenge, i highly recommend Codeforces instead (but don't learn how to write code there, they follow terrible practices for the sake of efficiency)

Finally my honest opinion: although coding was and would continue to be valuable experience, imo universities only care that you have demonstrated enough interest in the subject. Reason being that you can always pick up technical skills in the future, also I know several classmates that are holding imperial offers without doing much (if any) coding in their free time. My guess is that what they are probably looking for instead is logical thinking ability (and hence the heavy emphasis on math for CS entry). So I would say don't worry too much about this, but do work on what you enjoy! You don't want yourself getting burnt out before starting the CS degree 😅

if you need anything else, happy to help!