I (31) am eight years older than my BF (23). It works for us, but it' hasn't always been the smoothest road to travel. Here are some things to get used to.

(Preliminarily, make sure he's actually into you. He may be interested in hooking up or hanging out but not looking for a romantic relationship. If he seems lukewarm about it or not that into you, take that as a sign and look elsewhere.)

First, pop culture. My boyfriend's childhood happened while I was in high school or college. I was a stupid teenager who was "too cool" for the cartoons he loved growing up and the books and music he liked were "for kids" when they came out for me... I had to just get over that. At the same time, I'm frequently tempted to talk about or reference a bunch of old shit he doesn't understand or care about and I will always keep talking about it like it was the greatest shit in the world. You'll be in almost the same situation.

Second, life experience. You're either just out of high school or still in college. He's been working, paying rent, worrying about health insurance, and buying his own groceries since before you went through puberty. If you're in the U.S., you cannot even drink alcohol or go into bars or dance clubs legally yet. He's just going to have done a lot more shit and have more (and probably more nuanced) opinions. He probably hasn't studied for an exam or taken a quiz in at least six years. Maybe 10 if he didn't go to college. Those differences will mellow out in a few years when you turn 21 and when you get out of school, but you will need some extra empathy to relate to each other's struggles.

Third, expectations. You'll need to talk a lot about your expectations from a relationship. If you're single at 28, you've probably been seriously dating around for, what, maybe 10 years? He will have a lot more expectations and experiences shading his thoughts about how your relationship would work out. You will both need to talk more about what you want and expect out of your relationship, what your expectations are for (non-)monogamy, how often you should see each other, how you'll communicate ("What the hell is WhatsApp?"), and so on.

TL;DR---8 or 9 years is a pretty significant age difference at this point in your lives. It's workable but it'll take serious effort, loads of talking, and a lot of patience.