is it considered an outdated technology

It's definitely outdated. I can't think of many stores that actually still take checks as payment. It's not unreasonable to assume that this kid has never seen a check in their life.

Think about it. They're a sophomore in high school. They're around fourteen or fifteen; they were born in either 2000 or 2001. The iPhone, for reference, was released in 2007. It's entirely possible that this person's life has been, for as long as they can remember, entirely digital. You can sort of figure this out by the way they talk about a checkbook as a novelty that they can't use, which is what caused the whole conundrum in the first place (assuming this is not a troll, which is entirely possible).

It's interesting that you bring up what you learned in school. I was born in '92^*, and I remember taking a class like that in both middle and high school. While this is definitely on the tail end of Gen Y (or the middle, depending on who you ask), I've already noticed a very clear disconnect from the new generation. I'll be going into teaching soon, and this disconnect scares the shit out of me. I don't think it's bad or any worse than any other generation, mind you, but I'm definitely interested to see how everyone else adapts to fit the needs of a generation that has never been without immediately accessible technology.

^* I'm not trying to sound like some le old soul (oh no! I'm 23! so old!). I know I'm young still, but I didn't have a computer until I was 14, and I didn't have any sort of smart device until I was 20. This also was the norm for most of the people I went to school with. So, I may just have a warped and narrow perspective on how other people grew up.