I DON'T UNDERSTAND WHAT ON JUPITER IS GOING ON LIKE WHAT IS SHE 29 OR 12 CUS I AM NOT UNDERSTANDING... i need more now
Well, she was never 12. Middle school in Japan starts in in the what would be 7th grade in the US. So at the beginning, she would have been at least 13, and by the time she time-skipped or whatever, she was 14, because it was right before graduation time and the beginning of the next school year.
The real question is what is wrong with the translation of the age gap between Rinko and A-Chan in the first place. It says they are three years apart, making them both 1st years in their respective grade ranges at the beginning. This is kind of confirmed when one of the teachers tells A-Chan "I'm expecting you to be at the top in senior high, as well." Then, somehow, at the end of Rinko's first year of middle school, A-Chan is GRADUATING? That shouldn't happen until Rinko's THIRD year of middle school! So, when she goes to visit her at college, she should be a first year high school girl, not a 2nd year middle school girl.
Looking at the way the artist draws Rinko at 14 and 29, it looks like they do a fairly decent job of not making her change height too much, which is good. Most 14 year-old girls are past puberty and have, at most, a few centimeters of growth left before they are done growing, if that. (Many are done developing in other ways as well, unless they gain or lose weight, have a child, etc... but it is almost unheard of for a mangaka to NOT have a girl in a story like this have larger breasts in her grown up form...)
In any event, at this point I have no clue where the story is headed. That is a good thing sometimes... I haven't decided if it is because this has well written plot twists or if it is just all over the place...