What would I take to disprove the critical period hypothesis?

I'm a huge believer in comprehensible input hypothesis, and believe that I will eventually reach a native or at least near native level from it eventually.

I started learning Japanese after the age of 18, and I barely knew anything in it. Only the bare minimum greetings and stuff. No grammar, probably like 15 words total, and didn't know any grammar points or kanji before starting out.

Now I can read and listen without translating back. Doesn't that kind of prove that regardless of the age you can learn a language pretty well? What would it actually take to disprove the whole theory of critical age hypothesis? I understand that just my own personal anecdote won't actually change anything, but I just wanted to point out why I didn't believe in it.