What you could do is add date to the attribute you are using in the date picker. This can be set by using the [%BeginOfCurrentYear%] placeholder.
This can be done as a default value or as part of a microflow calling the page that shows the datepicker.
I don't really understand what your question is or what you are trying to achieve. There is a variable called [%BeginOfCurrentYear%] you can use when creating DateTime variables. Maybe you can rephrase your question, or post it in Dutch as well as in English, just to make sure we understand you clearly :-)
I have created a microflow to resolve my problem.