Well, that's why I said we need to distinguish between the age gap (which certainly not unheard of, though usually with an older, more powerful man and a younger woman) and the age Macron was when the relationship started, which is the real issue.
I say again, his parents and extended family knew from very early on. I have no idea whether they investigated prosecution, but I assume there were no grounds -- the age of consent in France is, I think, 15? though from what I remember there's a specific clause which prohibits sex between someone over the age of consent with someone who has authority over them.
They sent him off to school in Paris for his final year, presumably in part to part them, but clearly it didn't work. After that he was an adult living independently, capable of making his own choices, however unwise his parents might find them.
I think the description of Brigitte Macron as a 'predator who still has her prey' and the suggestion that Macron is a stunted, damaged, immature adult is a bit mad.