Average age of customer in Socar

set @startdate1 = '2019-01-01';

select avg(A.age) from

(select
distinct r.member_id as mid,
m.display_name as name,
m.email as email,
YEAR(r.start_at) - YEAR(m.birthday) as age
from reservations r left join members m on m.id = r.member_id
where r.return_at + interval 8 hour >= @startdate1
and r.state in ('completed','inUse')
and m.imaginary in ('normal')
and r.member_id not in ('125', '127')
and YEAR(r.start_at) - YEAR(m.birthday) < 100 ) A