The date picker uses a front-end library called Pikaday to display a UI to pick dates from.
As of Umbraco Forms 4.4.0 we have added the support for the Pikaday date picker to be localised based on the page the form is rendered on.
To achieve this, a Razor partial view is included - you can find it here:
This includes the Moment.js library to help with the date locale formatting & the appropriate changes to Pikaday to support the locales. If you wish to use a different DatePicker component this is the file that you would customize to your needs.
Configure the Year range
The Date picker has a configuration setting to control the number of years shown in the picker. The default value is 10 years.
You can find the settings for changing this configuration in
<setting key="DatePickerYearRange" value="10" />
value to a higher number (e.g. 100) to increase the numbers of years available in the Date picker.