I have a formula field, "Age", that caluclates the ages of our clients.  Age is set up as a text return type and has this formula:
IF(TODAY() >=Date(YEAR(TODAY()), 
MONTH(Birthdate), DAY(Birthdate)), 
TEXT(YEAR(TODAY()) - YEAR(Birthdate)), 
TEXT(YEAR(TODAY()) - YEAR(Birthdate) - 1))  

I want to create an "age range" field, so created another formula field with a return type of text, but keep getting the error:  Error: Incorrect parameter type for operator '>'. Expected Text, received Number.  Here is my formula:  

IF(age__c>"18","19+",
IF(age__c>="15","15-18",
IF(age__c>="10","10-14",
IF(age__c>="6","6-9",
IF(age__c>="3","3-5",
IF(age__c<="2","None"))))))

I get an error too if I try to change my age field to a number and try it from that way.  

Thanks for any help!
Kris