pl/sql function to populate dimension table

table Customers 

ID      NOT NULL NUMBER       

NAME    NOT NULL VARCHAR2(50) 

DOB     NOT NULL DATE         

EMAIL            VARCHAR2(50) 

ZIPCODE NOT NULL CHAR(5) 

Customer_dim

ID      NOT NULL NUMBER       

NAME    NOT NULL VARCHAR2(50) 

DOB     NOT NULL DATE         

EMAIL            VARCHAR2(50) 

ZIPCODE NOT NULL CHAR(5) 

AGE   NOT NULL NUMBER  

AGEGROUP  VARCHAR2(7)

i need a pl/sql funtion to pull the information from the CUSTOMERS table and populate the 

CUSTOMER_dim table  with an age in numbers and the age group in words. 

the age groups are as such :

11-20 = group1

21-30 = group2

31-40= group3

41-50 = group4

51-60=group 5