So how old Saiou is
I am going to try and explain what we know of Saiou’s age, just so it’s somewhere. And no, we don’t have any official information on that matter, all we have are hints from the anime.
In the sub, the only time someone refers to Saiou’s age is here:
(fansub from @kaiowut99 )
Where Chronos notice he’s young for a manager upon meeting him. It’s not so much the manager part that matters than that Saiou is visibly young. So we know that, in-universe, Saiou does not look like and adult.
Following that aspect, we can notice that in season 4 he looks significantly different.
Meaning that he is, indeed, at the end of his growth. The last thing we know is that, 10 years before, when he met Edo, he was still a child or teenager (no there’s no way to tell more precisely based on visuals).
So, given all that, we can give an age range: something around late teenagehood - early 20s. 17-24 maybe. Pretty much the same range as Ryo or Fubuki. You could go for the upper limit or even a bit higher by giving an explaination to the growth delay (transition, effect of the light...) though there is none in-canon.
Now, all this is in the sub. The dub change things a little. (And I don’t have screenshots for the dub because I don’t have access to an english dub with subs).
Chronos’ comment is removed. Season 4 doesn’t exist. Instead, we have Chronos commenting in ep 73 “he’s a bit older than our average freshman” which I take as meaning he does look like an adult in this universe.
Finally, while we do have the flashback up there (where Saiou talk about his premonition), we don’t have the ones from the graveyard. So this one could be anytime after. Still, Saiou was still a child or teenager when Edo was a kid. So he could be pretty much anywhere in his 20s, likely between 23-27.
So how old is Saiou? It entirely depends on what canon you want to follow. If you’re more into the sub canon, he’s a late teen or very young adult. If you’re into dub canon, he’s a young adult.
And if you’re wondering how that’s possible with how he looks, the truth is he only looks old because of his terrible health. Once he’s not looking like a walking corpse, he does look younger (and very cute).
