select stored mysql date and current date and compare it in months

Actually i am creating recruitment portal in which the candidate cannot apply again in 3 months. After 3 months he/she can apply. so i need to know how to do this. when candidate fill up form, the form date is stored in mysql database using current time stamp. now i need to compare the current time and database time, if difference between both date is greater than 3 months then only values can be added to the database.
In short the candidate cannot fill the form again in between 3 months. if the 3 months are completed then candidate can fill the form.