No - you cannot do directly what you are asking.

However, there are multiple ways around it:

Code:
CASE
   WHEN patient_age BETWEEN 1 AND 14 THEN
      'less than 15'
   ELSE
      '15 or over'
END
OR

Code:
DECODE ( TRUNC(patient_age/15),0,'less than 15', '15 or over')
- Chris