This Query relates to the School Type you have entered on the School Details table on ScholarPack. You will find this at Admin > Config > Core Setup > School (or by clicking on your school name at the top right of your screen).
There should not be more than 5% of pupils on roll outside of the age ranges specified for the School Type when the DOB is calculated on a DfE specified date.
Click on Edit to amend the School Type entered if it is not suitable for your student ages and year groups, then Update at the bae of the table to save.