The correct way to interpret "Heisei man" would be operating under (outdated) social norms common in the Heisei era in the same way Boomers do. Just read it as "old fashioned".
That was surprisingly forward for her to drink his drink. After reading the webcomic it seems fine but for just the second chapter in the serialisation it's a bit jarring for her character.
Makes sense that it's moving faster. It's a full comic now, so the chapters are longer.
I can also see the author being pressured to not drag out the story rather than a web comic's freedom of taking it at whatever pace they want.
pag 4:
Basically a boomer, wait, what?
"Baby boomers (boomers for short) are the demographic cohort following the Silent Generation and preceding Generation X. The generation is most often defined as individuals born between 1946 and 1964, during the post–World War II baby boom." So... No? He is a millennial.
Huh?! Basically a boomer?
What are you heck are you then? Born in 2020?
FFS, get your facts straight before you go calling Generation Y & Z "boomer" while skipping past X from the baby boomers. https://www.kasasa.com/articles/generations/gen-x-gen-y-gen-z
Showa is boomer... and gen x,... and millennials. Heisei is like a mix of gen s and the generation after that. I would say Heisei is more of saying “youngster” in this case.