I'm 28 now and I still think my 8th grade thoughts were pretty big time stuff and still guide my scientific explorations. So don't discount your thoughts because you're young.

In my experience, what you're feeling is a sense of knowing the general pattern of things. This is different than knowing every last detail. You probably don't notice this right now because you aren't facing many tasks that require huge amounts of precision.

Most of these tasks are boring and so you'd gloss over them as an 8th grader. But one day your boss or a professor will ask you to model some obscure thing to ridiculous sig figs. And you're going to struggle because you don't know how and probably don't even want to know how.

Learning to deal with failure and simply not knowing stuff is a critical life skill. Don't miss out on learning it. Sometimes it's tempting to stay in your comfort zone and play with familiar and interesting ideas, but that'll stunt your intellectual growth. You have to branch out until you feel like you have no idea what you're doing. The sooner the better.