From the current view (Layout view), group this report by values in the DOB field. Change the grouping to group by year instead of by quarter.
a) Remove the grouping and manually regroup the report by year values.
b) Access the Grouping properties of the DOB field and adjust the grouping level to Year.
c) Apply a filter to the DOB field to show only the year values instead of quarters.
d) Switch the view from Layout to Design, then select the DOB field and modify the grouping settings to group by year.