Is this person talking about death?

I think what she was asking is, "What if the good years are over before high school even ends?"

It's not uncommon at all that people feel life is downhill after high school. It sounds like she was suggesting it might happen even sooner.

Yes, you should be. I recently got out of depression, and it's incredible how people don't realize. For example, i live in a building, and I casually said to my brother: wouldn't it be cool jumping off? And he progressed on the conversation. You should talk to them. Best case scenario, he is alright and it was a misanderstanding. Worst case, they are actually bad and you will be able to help them.

Sounds like some nonsense, it would make sense if this is coming from a person in high school (mind hasn't developed yet).

Doesnt hurt to ask them

It's hard to say. It could be them being afraid of dying young, or it could be that they think the "fun" part of life ends before high school does, if that makes sense (which, my two cents is that it doesn't even begin until AFTER high school).

Existential crisises hit hard in highschool.

Maybe she thinks we're living in the end times? Maybe she thinks being a teenager in high school is the pinnacle of her existence?

I remember having such difficulty imagining what life after school would be like, especially since my college dreams were looking less and less likely, that I imagined that a time loop would occur at the end of the last year and I'd be back in first class all over again. And I'd spend an eternity in school. I didn't believe it would happen obviously, but it was a daydream that I used to think about a lot. Maybe she's thinking something similar for similar reasons?

She might have a learning disability.

Which could have been helped with more high school...

Reminds me of the type of thing where someone's thinking, like, "What if the Axis won WWII," or, "What if the Anglo-Saxons beat the Normans, rather than being beat themselves?" It sounds like just a regular old question that someone is thinking about.

Nothing to really fear about.