I would say that everybody starts out with a genetic baseline of stupidity that can never decrease, but it can increase due to environmental factors.

It’s not like there’s a hard and set rule, but everyone has some stupidity. Remember that stupidity is not ignorance. Stupidity by definition is “a lack of intelligence, understanding, reason, or wit, an inability to learn. It may be innate, assumed or reactive.”

If you are cured of your stupidity, then either something has happened to you physically to increase your intelligence, like perchance you had a blocked artery in your brain that was freed, and therefore the new blood flow has unlocked increased mental faculty, or your stupidity was based in ignorance, which is not stupidity in and of itself despite being a stupid thing.