Maybe? IIRC the anime doesn't specify an age for any of them either directly or indirectly, nor does it focus on anything to do with their school. If they are it's not really reflected in the art or writing, and the only character that definitely is has an extremely conservative wardrobe and is never the target of the weird horny shit - although she's still involved in weird and actively disgusting things too.

That said, the dubious ages are one of the reasons it's a solid "I do not recommend this" alongside a bunch of other weird and gross things about it, there's just also a surprisingly decent story at its core and it's not as bad as it looks for reasons that are hard to articulate. I think it's the all-female cast and how they're written to have agency and be the sole drivers of the plot - even if that plot is horny and gross - instead of just being passively present as fan service alongside a male-driven plot? It's like Kill la Kill vs some tripe like The 7 Deadly Sins or Overlord. Also the fact that it's completely unambiguous yuri with relationships that are weirdly positive and healthy compared to, well, everything else that's happening in the story.