I work in the insurance industry in the UK - we USUALLY use the
YEARFRAC function for this - this requires that you use the tools menu,
add-ins to add-in the Analysis toolpak, but it then makes the return
nice and easy - yearfrac gives an exact value, but can be modified to
return years and months by multiplying the returned value by 12, taking
an integer of it, then dividing back by 12!