An interesting, well-written piece clearly informed by personal experience.

As for me, I ask two questions:

1) Is the person over the age of consent?

2) Is the person consenting?

If the answer to both questions is yes, then I consider it none of my business, regardless of age gaps and whatnot.

Yes, people can and do make bad choices at a younger age. I notice you mention the thing about people's brains not being fully formed. What is the answer, pragmatically? Raise the age of consent to 25 (when brains supposedly stabilise)? Because if so, I suggest we also raise the age of voting, the drinking age, driving age, etc, etc. Either we treat people like adults at 18, or we don't.

Here in the UK, the age of consent is 16. Personally, I'd favour raising the age to 18 (bringing it into line with voting age, etc), with exceptions for those around the same age under 18, so as not to criminalise teenagers. That would at least keep predatory adults away from high schools and the like.

Beyond that, I don't see what else can be done, except social (rather than legal) disapproval, if indeed one disapproves. That would depend on a case by case basis. But even then, it brings me full circle to my main point. If the two people are over 18 and consenting, it really is none of my business.