Speaking from experience I say RUN! lol. Seriously though, when I was 19 I got into a relationship with a 26 year old guy. Now, that's only 7 years difference and we broke up this past December. When he turned 30, everything changed, and not in a good way.
After 5 years of loving someone who would never fully allow themselves to love me back, I have realized that there were many indicators that I should have ended the relationship a long time ago. He left me because he wanted a wife and kids, *RIGHT NOW* and I want a Masters Degree.
Well, he started dating someone 2 weeks after we broke up, she works with him, (Gee, I wonder how long *that* has been going on for) and she is 24, only a year older than I am. He also cheats on her with other girls at his job, and still asks me for pictures of my tits. (You know, to remember me by.)
I guess my point is this:
At 19, I was mature (as i could be for 19), and didn't really want to go out very much, really all I wanted was to be loved by someone. I had not had many positive relationships (How could I? High school is meaningless, and I was only 19 even though I felt older, I didn't have the life experience) and here was a MAN who was totally interested in me like no one ever had been before. I was swooning, and I loved him from the start.
The truth of the matter is that he was not as mature as I thought he was, and still isn't. He has a dirty habit of porn and asking women online for pictures of their tits, to trade for pictures of his penis, while he detaches himself from the relationship and doesn't have sex with me. He also used to balk at me asking him to do any housework (we lived together for 4 of the 5 years) even though he says he wants kids and a house, he wouldn't do jack shit without an argument, because he works full time, and I "Only go to school, so have no reason to be such a slob."
But did I know that in the beginning? Did I know I was in for a broken heart? Did I know he was so twisted up inside? NOPE. I 'knew' that he was sweet, bought me things, told me I was perfect and that he loved me and wanted to marry me. I "knew" that I was the most perfect girlfriend he ever had, and that he was insatiable in the sack.
I believe that I will always love him, a part of me at least, because besides all his faults we were best friends, we did talk, we did love at one point or another, he was my world, and he was my first real love.
But I would have to go with the other girls on here who question why a 30 year old man would want to be with a 19 year old, since I dated someone older, and in the end, our interests differed so greatly. It turns out I am much more multifaceted than he is, because he at 26 was who he was going to be forever, and I at 19 was a limited version of myself.
Anyway, I wouldn't be serious with him in any way, and my advice is to stay away from the situation all together. In 5 years, you will be different in a lot of ways, and he may be exactly the same.
Sorry for the ramble, lol