translation felt weird in some parts, so I checked the raws
Regarding the antiques:
In page 16 the line is 危ない骨董品が!(abunai kottouhin ga!) which would be "Watch out! The antiques are...!"
In page 17 the line changes to 危ない骨董品が!? (with revised reading as abunai vintage ga) The word "antiques" is replaced with "vintage" referring to her panties looking plain/old, hence her explaining why she's wearing such. Rather than the exact same translation (which makes no sense in this context), it's more like his thought is "Dangerous vintage (underwear) are (in my view)...!?"
Regarding page 22-23, the translation felt a bit rough. His full speech is more like: "Even if... she gave her consent... or even if she initiated it... or even if she teased him by calling him a pervy teacher... or even if she were to call him a masochistic pig and tell him to let it all out while counting down and teasing his nipples..." "It's a teacher's (adult's) responsibility to ABSOLUTELY NEVER lay his hands on his student!"