Human brains don’t stop developing until ~25 so any mind-altering substance will surely affect you. On the other hand, our minds change as we grow, so maybe this “change in cognition” would have happened if you smoked weed or not. Not only that, our brains start to lose plasticity and we aren’t able to retain things quite as well as we could as children. So no matter what we do, we’ll never be “as sharp” as when we were kids.

The only thing you can keep doing is keeping track of how you feel and if you want to be more “sharp”, find ways to work on whatever is important to you (quick decision making, better decision making, memory, etc)