how to set date field not to display past date
You can use the Field validation module to create validation for the date field.

You can follow below step to achieve this.


Go to  Administration -> Structure -> Content types and it will
display the list of content type.
Click on 'Manage Fields' links for your content type and it will display the list of fields for your content type.
Edit your 'Date field' from the list of fields.
Select '0 years from now' from the drop down 'Starting year' under 'More settings and values'. It will not display the previous year date in the popup.
You can set the default values for the date field under 'default values' section.
Save the settings.
Edit again your fields.
Click on 'Validation' tab in top of page.
Click on 'Date range2' link in the page.
Select 'value' from the drop down 'column'
Select 'Cycle of date' as global and set '-0 day' for the 'Minimum
date' textfield. Now, it will generate the error if date is less than today's date.