There’s an upper limit to your brain’s actual processing abilities, i.e how quickly you think and how you typically respond to certain things. That kind of stuff is genetic, which is why certain disorders like ADHD are hereditary. But that doesn’t mean you can’t learn as much as possible and maximize your ability far beyond what it could be otherwise.
It’s a bit of a retarded analogy, but instead of your brain being a mclaren f1 going 200mph, it could be a semi truck going 100