if i want to go to prom dressed like a dude from victorian era, why is that so wrong?

It's not really wrong at all it just might bring unfortunate results. In my school days it was the thing that made kids different that got them picked on and that's a pretty big target to aim at. It's also a very public event with all your peers you are stuck with them. You have to see these people again. I get that these things have changed somewhat but how much?

It seems in adults this softens up a lot more even if it doesn't disappear completely. So know you have that too look forward to if nothing else.

There is nothing wrong with you dressing this way. The question you need to ask yourself is it going to be good for me to express myself that way on this particular occasion? That's something you're best suited to evaluate.

Anyway I'm sure you'll look very... dapper seems historically context correct I think lol