User blog comment:Imperial Wyrm/Draw young versions of DBZ characters/@comment-5718774-20150924022928

We don't know when Bardock got the scar in his life, I just think he would have gotten it when he was older than 12...maybe during the Saiyan Tuffle War. Depends on how old he was in Age 737 when Planet Vegeta was destroyed (we never know his birth date).