Hello, this is Tsukishima-02. Nice to meet you.
I'm new here but I'm a long time fan of Master Teaser series and read it since the manga was first published. Never serious about it since lately though.
Anyway, I want to share my analysis on characters' ages in (Moto) Takagi-san spin off.
First, Takagi (former), Nishikata, Mano, Nakai, etc's ages are never revealed in the spin-off. Most fans made an assumptions by just adding 10 to their ages in the original series. By citing Takagi's "it has been over 10 years since those days in middle school" quotes in Chapter 31, assuming they're around 21 to 24 year old (11 to 14 + 10 = 21-24).
However, this is a very common misconception among fans as it is flawed as logic.
In Chapter 31, Takagi actually mentioned "it has been over 10 years since those days in middle school" while reading through her middle school graduation album. (In the original JP text, it can be roughly translated to "It has been over ten years since we were in middle school").
- The phrase "it has been X year since...", is logically used AFTER the event mentioned had finished. This made the counting need to start "after" she graduated in third year of middle school and earn graduation album, also, the age students graduate from middle school in Japan is 14 - 15 year old.
- Then, as referenced from quotes above, add over 10 years to it. "Over ten years" has a meaning in context equal to "more than ten years", which is not "ten" but "eleven, twelve, sometimes twenty and more" EX : "I have over ten years of experience".
- Thus, 14 to 15 plus over ten is easily about 26 to 27, meaning these characters are now 26 to 27 year old, at the very least.
Also, given the fact that Nishikata is now a full-time P.E. teacher, which required an official license and a specific bachelor degree plus a great reputation from a society to be one, be it an assistant teacher or not. He is also currently shown as (probably) the sole money-maker of his family, and earned enough money to rent/buy a mansion, can rent/buy his own eco car, afford own parking spot, even raised a 4 to 5 year old daughter.
And Mina already had three kids. That wasn't easy tasks to do, even in a rural area of Japan they appeared to live in.
All this had proven that the previous assumptions (age 21 - 24) among fans = completely false.
I hope moderators here considered these facts from the series and fans to agree with this analysis.