You can force the responder to pick dates in the future or in the past by enabling the Only allow dates in the past? or Only allow dates in the future? options. This way you can ensure that your responder's birthdates are not in the future or they do not accidentally schedule an event in the past.
The date picker menu can either be native to the platform the respondent is using (e.g. using Google’s date picker on Chrome) or can inherit from the dropdown menu styling.
In order to change the styling of the date picker, you can go to the style tab with the question selected.
Setting a date answer with URL parameters
Answers for the date component can be passed in via URL parameter, with the format as YYYY-MM-DD. For example, if you want to pass in the appointment_date answer "Apr 25 2023", append ?appointment_date=2023-04-25 to the flow URL.