Japanese High School year starts on 1st April with everyone aged 15. This is 9th grade. (It's different to the USA). During this first year they will all turn 16. During 10th grade they are all 16/become 17 and during 11th grade they are all 17/become 18.<br/><br/>So you can start the calendar either in (say) September of 9th grade and assume everyone by then has had their birthday (we all begin aged 16) or begin the game calendar at any point in 10th grade where we can choose between 16/17 or at any point in 11th grade for 17/18 year olds.<br/><br/>So first, decide the grade and the date, that dictates our chars ages ;)<br/><br/>BTW the first trimester is April to July, the second is September to December and the third is about January to March. ;D