First of all, I have to admit that, number one, if you live in a Western Society (such as the US, Canada, Western Europe, etc.) I find it really odd that a man would approach your father rather than you to express his interest in you. In my opinion, he should have tried to strike up a conversation with you first to even learn if his attraction for you stemmed beyond the merely physical and to give you a chance to discover whether you found him interesting or attractive.
Then, after a few conversations with you, if he was still interested in you and felt like you might be interested in him, he should have asked you out on a date (giving you the full opportunity to say no) and, if he wanted to, he could have sought out your father’s approval of that date or potential date before or after he asked you out. I can understand a man wanting to have the approval of a woman’s father before dating her in the hope of minimizing familial tensions, but the idea that somebody should approach the father as some sort of merchant or marriage broker for the daughter is one I expect to see in 3rd world societies or historical fiction books, and, frankly, that idea can stay there.
I also think that a 16 year old girl going out with a 28 year old man is awkward. A 16 year old and a 28 year old are at two totally different stages of development. Biologically, a 16 year old girl might be called a woman, but, especially in a modern society, she is not going to have the social, cognitive, emotional, and economic maturity that she would need as a wife and mother (at her age, pregnancy would be quite risky, too). She is also going to have completely different interests than a 28 year old man. In my opinion, 28 year olds need to find adults around their own age to marry, not attractive teenagers.
I also honestly think that your father should have stopped playing matchmaker as soon as you made it clear that you weren’t interested in the man he was trying to pair you with. It’s annoying when parents, siblings, and friends feel the need to pair young women (or young men) with somebody they think will be perfect for that young woman or young man even though that young woman or young man has made it plain that he or she isn’t romantically interested in the person continually being mentioned. I think parents (and siblings and friends) certainly have a right to make suggestions about somebody whom they think would make a good mate, and to express that they think a potential mate has some serious flaws, but they should acknowledge that the ultimate choice of who to marry and date lies with the young man or young woman in question. People who are single don’t need somebody to constantly try to pair them up with a husband or wife, especially if that single person is 16 and, in a modern country, really doesn’t need to be thinking about marriage too much.
I just have to say that I would find it so awkward (and infuriatingly condescending) if my father in all seriousness proceeded an introduction to a man with the statement that man wanted very much to marry me, because how could the man possibly want to marry me for anything beyond the superficial when we have obviously never spoken to each other before and certainly haven’t interacted on a level deep enough to decide that we want to spend the rest of our lives together.

It would just boggle my mind, and I wouldn’t even know how to respond.
I have to confess that I think your sister is right. A 28 year old wanting to marry a 16 year old is, in my opinion, pedophilia, and, at least in the US, a 28 year old having sexual intercourse with a 16 year old is statutory rape (i.e. a crime) and, last time I checked, rape was condemned by the Bible.
In answer to your questions, no, a 28 year old marrying a 16 year old is not acceptable, especially not in modern countries, and you have every right to refuse that match. Your father should not be determining your marriage prospects for you. You should respect his opinions about boyfriends and potential mates, certainly, as you should everyone else in your family’s, but you have the ultimate decision of whom you should marry. Make it clear that while you love and respect your father, you expect and insist upon the decision of whom you marry to be up to you.
At least in the US, you can legally never marry without your consent. You need your signature on some very important documents to make the marriage legal, and nobody is allowed to force you to give those signatures, and it is illegal for people to forge your signature on any of those important legal papers.
Most (if not all) churches will require that you consent to the marriage yourself. In fact, in the Catholic Church, if you do not consent freely to your marriage, that would be enough to make it invalid in the eyes of the Church. When you say, “I do,” you must mean it and not have been coerced by your family into making that vow.
Please, please familiarize yourself with the legal and religious protections that you have in your religion and in your country/state. It is never acceptable for men to abuse women in the name of religion or anything else. You are a human being, like any other, who deserves respect and love. You were created in God’s image as much as any man was.
As to your last question, it would only be the Biblical thing to marry the man your father picks out for you if that is the man that you want to marry, so that when you say “I do,” you can mean that promise with all your heart and soul without any coercion from family members. If your father pulls out the Commandment about children honoring their parents, remind him that the Bible also commands parents not to provoke their children to anger. Love and respect goes to ways Biblically:thumbsup: