Suisei's roommate's stated age checks out with what we know.
Here's her roommate's
pixiv account. She was in the art club in school. Her pixiv output stops in 2015. Say she moves to Tokyo from the sticks to try and become an idol. She'd have to work to make ends meet after that and so wouldn't have the leisure time to update her pixiv. 18+7=25.
Miko's roommate is 26. The duo is consistent with the fact that Suisei is the younger of the two in how they interact beyond just the ~20 day gap in debut date. So it checks out there too.
(I'm just guessing Anemachi's age based off how they interact. I'd say at least 2 years and at most 4 but it's just a guess. Anemachi feels a bit too doting for it to be just one year but they're close enough that I don't think it's 5+ years.)