Okay, this is awful.
Generation two aged up young adult early on his birthday (3 AM or so; I just wanted him to grow up). He moved in his girlfriend, and close to midnight, himself, his girlfriend, and another housemate went to France for six days and all was pretty normal.
Now they're back in Twinbrook, and it seems that the entire household forgot to age a day (why yes, I memorize everyone's ages; generation two is 21 days to adult instead of 20 like he should be, girlfriend is 10 days to adult when she should be 9, etc.). I have a pre-France save, for reference. And I saved, exited and reloaded to see if that made a difference.
No other life-extending measures could have been used, since all the life fruit is in the locked basement or in my immortal founder's inventory and other life-extenders are absent from the house entirely (no makeover stations, tattoo chairs, saunas, any drinks made with life fruit, anything cooked with life fruit, banned elixirs, stray ambrosia, etc.). While the girlfriend used the dresser, her age was normal right after it and no one else used it. The problem seemed to stem from France, if anything.
Am I doomed? I learned my lesson about traveling at midnight too.