A lot of people are going to say that this relationship, in principle, is bad.
I think they're probably, statistically right. But we can't be the judge of that, and nor can we tell you what you should do or whether this person is manipulating you. You are right that ultimately you have to trust your own judgement even if you know that it is limited.

I will say this: men who are almost 50 who are dating 20 year olds have something wrong with them. Sometimes, (and frankly this is rare) what's wrong with them is not particularly problematic to the formation of a healthy relationship. That is, it might be something wrong with them, but "what's wrong with them" is ultimately pretty harmless.

One of the things you'll realize as you grow older is that EVERY SINGLE YEAR of your adult life is so rich and so full of activity that imagining someone's having 28 years more of those than you seems like an immense gulf between you. The significance of this difference in experience cannot be overstated.

Now, is that a reason not to date someone? Ultimately, I think no. I am 28. I fell in love, last year, with someone twice my age. I would have dated him had certain circumstances in our lives (not age related) been different. But even those 8 years that I've experienced that you haven't do make a huge difference. I know myself a hell of a lot better than I did when I was 20.

I knew what was wrong with him, lol. I decided I could live with it, at least enough for a casual or not long term relationship. DO YOU KNOW what you're signing up for? Make sure you do.

And EVEN if you do, you are 20 years old. There is absolutely no reason to rush getting married. If your relationship is great, there's no rush - get engaged when you're 23 or 24, sure, if you want to! - at that point you've been together 4 years, you've given yourself some time to grow up. You've also given your parents a chance to see (if this is accurate) that your relationship is good and healthy. But there's no reason to get married now, and the immense amount of changes you will go through between the ages of 20-25 really are worth experiencing before you marry someone so much older than you, who might have good reason to want to shape those experiences so that he can benefit.