Custom "date" field?

I need to add a custom field for "Date of Birth" of customers.
I only have the option to create additional text field, How could I make a validation rule so users can only insert dates???

Hello,

I am sorry but we don't support the Date custom field type. You can only use the Text field type for that.

Sincerely, Giang

yes, but people simply insert "1989" instead of their actual Date of Birth....
Is it possible to create a validation rules like the ones alrady created for min_length or max_length ???
I tried inspecting the code but I couldn't find where to add a validation rule...

I am sorry but this is not supported now. You can try to insert a small label near the text box to guide user how to insert the correct format there.
Sincerely, Giang