I am retrieving the results from the db but they are not properly ordered. I need ordering to be done on two levels, if possible.

Code MySQL:
 FROM default_age_groups
      BY FIELD(age_group,1),'A','U','O'

here is the data as returned:

Up to 3 yrs
Up to 12 yrs
Up to 10 yrs
Over 65 yrs
Over 60 yrs
Over 55 yrs
Over 21 yrs
Over 18 yrs
Up to 5 yrs
As you can see it is not even ordered as I am trying in the query because 'Up to 5 yrs' is at the end. In any event, I need it to be ordered by A,U and O and within that, for it to be ordered by the numbers.

Can anyone point to a solution, please.