An invention of Lisa fails (again), and the siblings have different ages that they should have.
It's friday night and Lisa is making her new invention (the sixth in this season): the Age-Timer 5000. The idea of the product is, example: You are a teenager and you want to play at the McDonalds playground without being judged, so the Age-Timer 5000 does that. You put the age you want to have, and shoot yourself. Voila, you have 7 years now, go to play and re-enjoy your infancy.
Now Lisa needed a 'lab rat' to test the machine. Because nobody wanted to be that, Lisa shot herself, with the machine configurated at 10 years old. So Lisa made her a pre-teenager. After Lincoln saw 10-year old Lisa, he also wanted to be older.
So Lincoln went to Lisa's room, and turned on the machine. He adjusted the gun to turn him a 21-year old adult. This worked, so Lincoln could be capable of seeing R-rated films without actually waiting 8 years. Altough something don't got well, because when Lincoln leaved, Lola and Lana started fighting about the machine. Because the last person to use the pistol was Lincoln, the buttons maked his age changes. In the fight Lana presses the fast-forward button. So Lincoln started to getting older, and older (like the episode's title). When the button was un-pressed, Lincoln exited the cinema, as a 65-year old man.
When old Lincoln arrived home (with too much tiredness), the other sisters had different ages that they should have. The younger were older, the older were younger, etc. 10-year old Lisa arrived, and (because she still had her intelligence (rare, because usually you get dumber at 6)) tried to calm down the siblings. Now Lisa shot them with the machine, one-per-one. Including her, got back to a 6-year old kid. Now the siblings agreed to get rid off the machine. So Lisa puts it in the trash can.
When they leaved, 3-year old Lily went to the trashcan, and grabbed the gun. She started to press keys at random. But she makes the command '504'. And when she pointed to her head, and shot. She was only a mess of dust.
After noticing this, Lisa tried to undo the machine effects. So she created the Age-Timer 5100, which also has the capability of reconstruct people from dust. But the wind came, and it blowed the dust far away. So the siblings, with InaVacs 710 (innalambric vacuums), started suck everything in the air. Later they had all the Lily's dust. So Lisa put the dust in a jar, and shot it with the Age-Timer 5100. Lily had came back to home, alive, as a baby.