Who is the youngest person to ever play a "clerk" role in the series?
who refers to name; the youngest person refers to max(birthdate); a "clerk" role refers to role = 'Clerk'
SELECT T2.name FROM Credit AS T1 INNER JOIN Person AS T2 ON T2.person_id = T1.person_id WHERE T1.role = 'Clerk' AND T2.birthdate IS NOT NULL ORDER BY T2.birthdate LIMIT 1