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Children in the community were each given a bicycle for their use upon reaching the age of nine years. At that point, they were officially considered old enough to be responsible for caring for the bike, capable of using it safely, and old enough to begin traveling about the community to volunteer activities.
In fact, however, most children learned how to ride bikes sooner than the designated age - and did so, using bikes borrowed from an older sibling or a friend. Jonas had begun planning about how to go about teaching Lily how to ride, although she reached her eighth birthday during the course of the story.
It was one of the few rules that was not taken very seriously, and it was almost always broken. The children all received their bicycles at Nine; they were not allowed to ride bicycles before then. But almost always, the older brothers and sisters had secretly taught the younger ones one. Jonas had been thinking already about teaching Lily.