You can set default values and restrictions for your event's registration fields. This is done in the "edit registration" page via the pencil icon as seen below.
Different field type gives different default value possibilities:
Field Type: Dropdown
Field Type: Text
Field Type: Date
Unlike the other field type, Date field type allows you to select between a calender date picker or a drop down.
Attendees will also be notified if selected date ranges are outside of the defined values, upon submitting registration