Well, thing is the gender gap is largely over exaggerated (and accounted for by exit poll errors, I may elaborate more on this later). Married couples usually vote the same 95% of the time, it's just Single Mothers vote more D then Single Men which accounts for the Gap (the latter votes D to, but at like a +10 rate versus single mothers being at +20. I have a link on this, but can't post it do to not having enough posts.)
I'd contend that mass incarceration is a decent component the gap as well. Given that non-White males are the most likely to see their franchise restricted due to mass incarceration, the universe of Male voters is likely older and Whiter than the universe of female voters.
I think an end to mass incarceration would reduce the gap somewhat.
No, I don't think that's it. The gap exists with young people and people of color too, from what I see on the polls.
Yes. Black men for example have been trending Republican and most data suggests that it's due to the increasing gender gap.