I think this is a very interesting idea...no idea what studies would show, but it rang a bell.
My NMom was just shy of 40 when she had me. Before that, she'd had a very exciting life in Washington during and just after WWII. Those were heady times, she was a very well-regarded professional, a very proper (flirty in a proper way), charming and beautiful woman. She was courted. Ironically, she had grown up dirt poor, and my sweet and shy Dad, who grew up like Little Lord Fauntleroy--except without the ego--was smitten by her great confidence and glamour.
Hmmm. Soon after they married, she's "professor's wife", and stuck at home with the 2 kids until we get to school. She began working as a teacher the moment the youngest (me) started school.
So I wonder...if younger mothers might be somewhat less likely to be Ns, because they haven't been as long "out in the world" achieving independence and professional status? It shouldn't be that way, that a woman feels one WHIT diminished for being a stay-home mom, but we know it still is, in many people's minds. That's a stupid stereotype, but women still aren't fully valued and respected even when they DO turn into CEOs, or raise 10 fabulous human beings...in the world at large, they're still not fully respected. So maybe there's something about that before-children and after-children contrast that pours fuell on the N embers in women who are predisposed to the disease.
Hops