Thing is, mate, the timeframes for all those events are blurry at best and incomprehensible at worst. I know that Noriko and Maya are kinda in the same timeframe, but there's also Niki, Sekai, Ami, accident and all of that happened "some time ago". I wanna wait until we have some sort of stable ground to base our guesses upon, as to not get into discussions "what happened when" when we know fuck all about it. No jabs, btw, just observation.
I mean, we've actually been given a few ages and time frames, so I'm not entirely sure what you're talking about.
It's been 8 years since Sensei and Niki stopped seeing eachother:
After they dated for 5 years:
And Sensei is 31, while Niki is 29:
Ami was also 7 when her parents died, and should be turning 16 around the start of the game, since the likes of Ayane is 15, and Ami's bday is before hers:
This also means her parents died around 8 years ago.
Overall: The Accident, ghosting Niki, and considering there didn't seem to be much of a timeframe between this and tutoring Noriko and Maya, this all seemed to happen when Sensei was 23, 8 years ago.
It's likely why the number 23 comes up so often.
Tutoring also seemed to end almost 5 years ago:
So, considering Noriko is one of the older girls, while Maya is one of the younger girls, Noriko was likely around 12, Maya was around 11, and Sensei was around 27 when he stopped tutoring.
Then almost 3 years ago seems to be around the time when the space war started, Sana's brother died, Noriko last saw Sensei, etc, but this time frame is especially blurry with only really Noriko seeming to ground it: