I think it's a bit of a stretch to suggest he headed specifically to France because of their age of consent.
I think it more likely that they went to France because it's the nearest foreign country from here that you can get to in a car.
If it's all about age of consent, then why not head straight to Spain, where it's 13?
It's not beyond the realms of possibility that both he and she will maintain, if and when they are found, that there's been no sexual contact at all. No one will believe them, of course, but without proof there's bugger all anyone can do.
So it may boil down to kidnap.
I have absolutely no legal knowledge, btw, so I could be talking bollocks. Happy to be put right by anyone better informed.
Either way, it's a horrible, horrible situation for both Megan and her parents.