Date Difference between consecutive rows - Help Request

Student_id ReviewDate
123 14/04/2013
123 null
123 12/03/2013
123 18/02/2013
123 21/01/2013
123 20/01/2013
124 12/04/2013
124 07/04/2013
450 14/02/2013
450 12/02/2013

I have above student records I am trying to find the student who have not had a ReviewDate and these students who are due for ReviewDate

Every student Must have a ReviewDate after 7 days from last ReviewDate

ie student_id 450 is due for ReviewDate as is more than seven days since they had last ReviewDate. This is based on Today Date. 14/04/2013
Stuedent_id 121 they are ok as had last review date on 14/04/2013

I am using Microsoft Access 2007
I would like to get a report of these students whose ReviewDate is due based on todays date: or date which report was executed
I would like the report also to show the numbers of days since they had last review date(date difference)