In the period before the civil registration, which was introduced in most of the Netherlands in 1811, baptismal records are the usual documents to consult for information about the birth date of an ancestor. In most cases, children were baptized within days of being born. But some religions did not baptize infants but waited until people were old enough to make an informed decision about joining the church.
In the Netherlands, the main church that baptized adults was the Anabaptist or Mennonite Church. The church was named after Menno Simons (circa 1496-1561), a leader during the Anabaptist Reformation. In Dutch, members of this church are also called “Doopsgezinden.”
If you can’t find the baptism of your ancestor, try to find out what church they belonged to. If they were Doopsgezind, the baptism may not have been recorded until your ancestor was in his or her twenties.