You could give your character's birthday - just a one-time thing, it cannot be changed to prevent abuse - and around that day IC, your character will age up. Like my EU character's birthday is September 22nd, so technically, on September 22nd in the first year, she should turn 12. There are more people who have birthdays somewhere during the year and it's only until the next year that their new age shows, which could cause confusion in topics. My character age is technically 14 at this moment, but it'll show 13 until the end of the year.
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