As of July 2023, I've been having the same problem. I was into manage worlds for the first time in my new save (hadn't played for a long time before this so I can't tell whether it's a new problem or not) and when I went back to live mode and checked the calendar it was suddenly my sim's birthday. I was so confused because I check the calendar daily and I didn't remember noticing there was going to be a birthday any time soon. Then I unpaused and the next thing my sim did was aging up (at about 8 in the morning). I am certain my sim still had about 30ish days left in their young adult life when this happened. Now their life bar looks full and glowing. I exited without saving but I don't know what to do now. I do play on long life span and just really can't enjoy the game in normal life span so this has been fairly upsetting as all the solutions seem to be to set it to normal or/and turn aging off (but that would also remove a lot of important gameplay from the game especially in regards to neighbours). All the posts I can find on this issue seem to be from last year so I don't know if this came back with a recent update. I do not use mods and have never used them. Would like to know is anybody has found a viable solution.