To make the age of majority 21 or something? Maybe not related. I'll still never eat bugs for protein while their globe-trotting elites enjoy their steaks, but I digress.
I've always been at odds on child marriage. Not child marriage per se, but that marrying a child makes the love shared more legit. I don't believe the attractions of kids are not authentic. I think their feelings and those they love are very authentic. At the same time, I think their preferences change over time and with more references from life experience.
Generally speaking, marriage is expected to be a lifelong commitment, even if we all know the reality turns out much differently. It's still an idea which, if you hold it in high regard, should be reserved for people whose awareness and preferences are not in a state of flux. So it would seem to me anyway.
In this case you mention, and without knowing the person you name, I simply suspect it's more feminism in disguise. I have no idea, but that's the usual likely culprit in the US nowadays. They don't like men, their dads, or girl lovers.