So the argument is that Amy is not sexually mature and that Sonic character ages are analogous to normal human ages. Ok, so let's go by sheer logic to try and debunk this.
We know that both Sonic and Shadow are as mature as they're going to get, since while Shadow is designed to be at peak physical condition, and is literally 65 years old, he and Sonic are the same height. So we can assume that for male hedgehogs, 110cm is about as tall as they get, therefore they are mature at that point. Amy is only a few centimeters shorter than this, which would make sense given she's female, therefore shorter.
This is all on top of Amy not only having fully developed breasts, but being the same height as Sally (barely "legal" but still an adult, last I checked). Also, she lives alone, is perfectly independent, and nobody during the entire series across all media (except under Penders) has addressed or questioned her lack of legal guardian at all (unlike Tails, where this aspect of his character is occasionally brought up).
I'm expecting more than a couple people to reply to this and call it hoop-jumping, stretching, or some other dismissive Twitter term, but bottom line: Amy, for all intents and purposes, is an adult, and the ages are only really there to make these characters seem more relatable to real-life children. So, she passes the Harkness test. Are we done here?