1941年，奥尼尔出生于美国加利福尼亚州洛杉矶，他是女演员帕特里夏的长子，他的父亲叫查尔斯·奥尼尔，是一个编剧和小说家。他的哥哥凯文是一个演员和编剧。奥尼尔的外祖父是爱尔兰人和他的外祖母俄罗斯犹太人。奥尼尔原本在美国读书，并且练就了一身拳击术，后来他们家搬到了德国慕尼黑，他在那儿上高中。
Amick was born in Reno, Nevada, the daughter of Judy, a medical office manager, and Bill Amick, a musician. Amick's parents are German; the name Mädchen (pronounced [ˈmɛːtçən] ), which means "girl" or "maiden" in German, was chosen by her parents because they wanted an unusual name.
