It's been a century or more perhaps.
Maybe two? No one's sure anymore. Peaceful times do that. It dulls our sense of time, consciousness, anxiety, it erases everything. Even for those who have been forsaken by the so-called 'peace'; time has definitely dulled up.
Some say it was a normal day, some says it was winter, some says there was a storm that time. No one's sure anymore either. But ever since that 'day', nothing was the same either.
Children started to be born with anomalies. No, not the physical ones, but rather internal. It was some sort of chemical mutation in their brains, granting them different abilities. And apparently, these children were too much for the world. Society started losing its balance. They are called Saplings. No one knows why, they're just called that way.
Avalon floats mightily about a few thousand feet from the ground. It's an ideal haven of technology, democracy, and any kind of advancement in one. Its steel beams glint at the morning sun, the soft hum of the island's everyday hustle and bustle can be heard down below.
Despite it's futuristic and rich splendor, Avalon is actually a prison. A manmade structure created to keep the Saplings in one contained space. Through the glass walls, steel bridges, holographic displays, orphans with extraordinary abilities strive to survive the cruel world they live in.
And this has been going on for a long time.