I wrestled, am not religious, but I sure as hell would have been too shy to wrestle with a girl... not because of her, but because I was a BOY! It's frankly awkward enough to get into a 'onesie' with ear-cups and 'special' shoes with another guy at that age.
The important thing here is that he FORFEITED, he didn't whine or sue. He made a decision, or his parents did, but either way they did it at their own expense both socially and otherwise, not hers.
Still, let me put this out there: In professional sports you have a nearly universal (it seems) use of 'illicit' performance enhancing... let's just say "methods" at this point. It's a joke to think that there is ever an even playing field, so frankly if a woman (read: WOMAN) wants to wrestle with men (again, MEN), go for it. Win or lose, who cares?
I will say this: one of the most basic tactics in G-R wrestling is to make your opponent WANT to lose; you want them to stop bridging and be PINNED. One of the totally accepted ways to do this is to dig your chin like a freaking drill into your opponent's sternum.
1.) This is quite painful, and like many men, I was raised to avoid hurting women at nearly any, if not all, costs.
2.) At that age, sticking my chin into a girl's chest and digging might be a LITTLE awkward.
3.) Fireman's Carry, and a number of other moves just... damn.
Again, if a woman came to me now and wanted to wrestle, I'd decline, but I don't think it's wrong. In a tournament of adults, I'd take the challenge, but I'd be lying if I said that I'd use the same pain-compliance techniques. I could train myself to, but WHY?!... I LIKE having a serious reservation about causing women pain.
By the same token, fencing with women is the best practice you can get; they'll usually beat you. It's not a competition issue in my mind, it's about cultural asymmetries due to physical realities.
Besides... I guarantee that kid will be more concerned about, "unintended consequences" in the cup region, for him and her. You can't just throw away literally a lifetime of lessons and training and start manhandling a girl. You can try, but it'll just show you that in fact, you DO fight like you train.