I don’t think it’s ever too late to get better at something - even “good” artists in their teens don’t become “great” until much later. Why? Because they keep practising and keep challenging themselves. You need to try something different, rather than constantly doing the same thing, which I feel is what you’re doing now.
Try some art exercises. Just draw some bodies for now. Reference like a madman. Stop drawing your characters in neutral poses and start drawing them in dynamic poses. Anything! Just do something different.
Oh, I meant to respond here. I tried to give you advice a few times on how to improve/what to do with the art you showed me but it was often met with excuses or fell on deaf ears, so I decided to stop. Agreeing with what Agro said here, the foundations of art are essential for improvement. It’s never too late to start. Don’t compare yourself to other people, as tempting as it can be, because everyone’s art journey is different.
One step towards getting better may be to stop admitting defeat by resolving that you’re too lazy to improve; if you really want to improve, you can. Pick one thing you want to get better at and draw it over and over again. I’m not saying you have to start now either, because I know it’s hard to juggle school + art, but I think you’re fully capable of becoming a great artist if you put in the time.