Med hjælp fra Slet med Join i MySQL
Jeg lavede
DELETE FROM table_name a
INNER JOIN (SELECT count(name) as dupesPostMillenia, name
FROM table_name
WHERE dob>'1/1/00'
GROUP BY name ) b on a.name=b.name
WHERE a.dob < '1/1/00' and b.dupesPostMillenia=0
Jeg tror, det kan hjælpe.