Anabaptism
Anabaptism is considered a sect of Protestantism, but they refuse to baptize infants. Anabaptists believe that baptism should only be preform once a person is willingly able to confess their faith, hence the culture around teenagers figuring things out for themselves for a few years.
Baptism & Marriage
An Amish person will usually get baptized between the ages of 18 and 22. According to Amish rule, a person is not permitted to marry until they are baptized. When they do get married, it must be to another member of the church.