He celebrated his coming of age under the Imagawa clan in Sunpu, called himself Jiro Saburo Motonobu MATSUDAIRA, with a character (元: moto) in the name of Yoshimoto IMAGAWA (今川義元) awarded, and married Tsukiyama-dono, a niece of Yoshimoto IMAGAWA and a daughter of Chikanaga SEKIGUCHI.
駿府の今川氏の下で元服し、今川義元から偏諱を賜り松平次郎三郎元信と名乗り、今川義元の姪で関口親永の娘・築山殿を娶った。