Actually, if you follow the link for that quote, you'll see that whoever it was at Islamic Voice who wrote that answer specifically says that a girl should not be married off without her consent or before she's able to assume the responsibilities. But he still says the marriage is valid.
How so? did he explain why?
I can't see how its possible to consider it valid since the requirements were not met. Is he talking about this particular case having some exceptional thing that makes it so or in general?