Rumspringa lasts as long as an Amish teen chooses. Rumspringa refers to the period of time when Amish teens can venture outside the Amish community and live like typical Americans before choosing whether or not to join the Amish church.
Baptism marks one's entry into the church, but the Amish cannot decide to get baptised or join the church until the age of 16. An Amish person still maintains family ties and is not shunned if he does not return from Rumspringa. However, the vast majority do decide to return and make a commitment to be a part of the Amish community. A member who leaves the Amish community after joining the church is shunned and forever considered an outsider.