So... I think i have a grasp of why He wants his wife to be under 14, its cuz so they're not yet adults when things "end" with him, aint it? So they can still be fiancee candidates to other gentlemen when somehow he's out of the picture. "3 years" of peace as he foreshadowed. With the oldest possible he took into consideration would end up as 16 years old by that time. Like he knows he's on borrowed time so he wants to at least get close to a girl, and by the time he's gone she wont have that much damage to her chances of being remarried