Hi Khalil,
If you are developing on Studio Pro 9 you can use the function “calendarMonthsBetween” or if you are using older versions you can use the Java action “MonthsBetween” from the CommunityCommons Marketplace module in case calculating the period is required.
Or if you don’t need to calculate the period you can read the month from the selected date by using “parseInteger(formatDateTime($EnteredDate,'MM'))” and then validate the month.