
When Punpun takes place.
Near the end of the manga the birthday of Soara Onodera is 7/7/11. This is before the timeskip at the very end, and I assume Punpun is 22 post-timeskip (looking at the fandom page and punpun wiki).
Asuming this is the case, the storyline starts with Punpun aged 11 in the year 2002 and ends around 2013 (matches the end of the mangas serialization) with him aged 22.
This would also mean Punpun was born in 1991.
(Correct me if I'm wrong pls)