The entirety of Simpsons takes place in purgatory, where nobody ever ages. Think about it. There's no town that could physically exist that borders a desert, mountains, canyons, green forest, the ocean, and still gets heavy snow in the winter, and heatwaves in the summer.
Bart and Lisa are stuck in their child bodies, but they have adult desires, which is why they fuck each other.
Some characters just can't take it any more, and want to leave for good.
But as Chief Wiggum once said, the only way out, is suicide.