Okay, I'm going to be blunt here. This is for the OP.
There are only two reasons why a 25 year old would be with a 16 year old, and neither does him any credit. Either he is much more than usually immature for his age, and I'm talking about immature enough so that he should have a legal guardian taking charge of his affairs, or he is after one thing and one thing only, and it appears that he's gotten it. If her parents are sufficiently negligent as to allow this marriage to take place, she will soon find that she doesn't see her friends any longer, that she is rarely leaving the house and none of them are coming to see her, that's she's spending 100% of her time caring for the baby and tending to her husband's needs, and that his needs are taking up more and more of her time. He'll be angry if things aren't done precisely as he demands, and demands is the exact word. He will be controlling her every move and every aspect of her life. It's pretty much certain that if she puts up any kind of resistance at all, one of two things will happen; he will be physically abusing her, or he will leave her for another young girl that he still can control.
And yes, I know, he's not like that and she's much more mature than other 16 year olds and I don't know them and how dare I judge. Yadda yadda yadda. Heard it all before. Still stand by the answer.
If you care anything at all for this girl, you will report this relationship to everyone you can find to report it to and hope someone listens.