SQL Group by Age Range

SQL 2005, I have a table with a column 'ages_c', I need to group the records by age ranges. This is the query that I found on this site and it's getting me 90% there but the 'group by' is erroring, *Invalid column name 'age_range'*

 select 
  case
   when age_c <18 then 'Under 18'
   when age_c between 18 and 24 then '18-24'
   when age_c between 25 and 34then '25-34'
 END as age_range, 
 Count(*) as count
 from contacts
 group by age_range
 order by age_range

When I group and order by 'age_c' my result is:

  Under 18  1
  18-24 1
  18-24 1
  25-34 1

What I want is:

 Under 18   1
  18-24 2      
  25-34 1

Thanks.