Sort age with dateif formula - no leading zeros

The following works well with working out age to give age in years and months (eg 9 y 10 m)

=DATEDIF(birthday,date,"y") & " y " & DATEDIF(birthday,date,"m")-12*DATEDIF(birthday,date,"y") & " m"

My problem is trying to sort this column. Doing a straight sort goes by year then month
1 y 10 m
1 y 2 m
10 y 10 m
10 y 2 m
2y 10m and so on

Is there a way to format to give leading zeros so that the sort works the way I want it to?
Otherwise I may have to resort to writing a macro which will be tedious!

Thanks