How to get the value of max() group when in subquery?

So i woud like to find the department name or department id(dpmid) for the group that has the max average of age among the other group and this is my query:

select 
 MAX(avg_age) as 'Max average age' FROM (
    SELECT 
      AVG(userage) AS avg_age FROM user_data GROUP BY 
         (select dpmid from department_branch where 
            (select dpmbid from user_department_branch where 
               user_data.userid = user_department_branch.userid)=department_branch.dpmbid)
) AS query1

this code show only the max value of average age and when i try to show the name of the group it will show the wrong group name.

So, How to show the name of max group that has subquery from another table???