The most straight forward means of doing this will be by adding validation rules on the field in salesforce.  Of course that is a server side solution and will not prevent users from seeing the old date.  

Our date picker uses the JQueryUI DatePicker,  which has a substantial number of customization possibilities.  You can create a custom renderer that leverages the “minDate” function of the date picker.  See more documentation here. 

Thank you Rob, that works.
one more question, I want to restrict manual entry like typing a date value in the date field. how to restrict that here ?.
 In jquery I used to make input field readonly thats works for that,but here making field readonly from standard functionality doesn’t serve my purpose.