output.txt

    day     |   age
------------+----------
 2008-11-09 | 10 years
(1 row)

query.sql

SELECT
  date_trunc('day', create_date)::DATE AS day,
  age(now()::DATE, date_trunc('day', create_date)::DATE) AS age
FROM asset.call_number
WHERE owning_lib IN (
  SELECT id FROM actor.org_unit_descendants(
    (SELECT id FROM actor.org_unit WHERE shortname = 'TADL')
  )
)
GROUP BY day, age
ORDER BY count(*) DESC
LIMIT 1;