I take and pick my son up everyday from school, I couldn't even imagine being with a 16 year old. Geez, all this dude is doing is taking advantage of her 16 year old stupidity and she's (with her probable parents instructions) taking advantage of his bank account.
I'll ask this and let it go. Just because you personally would not do it does not mean that nobody should do it. I doubt you would want to clean toilets as a job for example. That takes care of your first sentence.
How is he taking advantage of her? If she stuck a baby in an oven, I think you would want her held accountable to her actions. I doubt you would accept the "she's younger than 18, so she doesn't understand the consequences of her actions." If you would not accept that line of reasoning then, then why do you accept it now? If you would accept that line of reasoning in the baby oven case, then at least you're consistent. So assuming you're inconsistent, let's say that she has the ability to know the consequences of her actions. She consented to the marriage, he consented, her parents are in agreement, so what place do you have to say no?
However, you may be right about the bank account thing. But that's a separate issue and is purely guessing since we have no evidence to support that claim.