@895489045890
Are you using any mods? Specifically, any mods that might affect aging or allow you to manually change anything about a sim's age? Like resetting the days within a stage, or changing the life stage or changing the length of a life stage? If you are, have you changed anything? You can try testing your save without those mods in the game. Don't save when you do so as to not mess up your save. If it doesn't happen when you test, then it is probably one of those mods and you will need to update or remove them to get things back to normal.
Hope this helps.