Why do you mention a 12 instead of a .410? There are gauges between. A mild 20 or 28 would be best.

It might be for other reasons, who knows, but both my brother and I were started on 20 ga guns and neither of us has or has had any issue with recoil. In my estimation, we learned early on that guns recoil and that it's a physically insignificant event. I think that a mild gun would have not prepared us for what 'real' guns shoot like. That's my guess, I can't prove it.