I'll always view it as dubious-con regardless of age just because it feels like he's under John's spell of obedience or something.

Hm. Yes, that's valid. For me, I agree it's dub-con because Dean's basically f---ed up when it comes to his dad, but if he's very young here, that would take it into non-con territory. If he's old enough to consent, old enough to be experienced...well, there are a couple of moments in the fic when he could end it, no harm, no foul, and he choses not to. But, as I said, it's creepy either way.

Thanks for commenting!