You have two basic approaches to consider:
1 )Use a calculation field with a case function to return the desired value.
Case ( Age < 61 ; 1 ;
Age < 71 ; 2 ;
Functions like this can be looked up in FileMaker help to learn more.
2) Put your ages and matching "scores" in a pair of fields in a related table. Use a relationship to reference or copy values from the related table into your original table. This second option allows you to control what values are looked up simply by editing the records in this table so this is a more flexible option if the "scores" are something that may need to change from time to time.
Thanks for your speedy response!