I don’t understand what the problem is. ❓ You’re 21 years old and a legal adult, so a 13 year age gap isn’t illegal or even necessarily a bad thing. While cougar relationships where women are older than their boyfriends, are [i]relatively[/i] new, women dating older men is pretty traditional.
I can see where your boyfriend working for your father could be a conflict of interest for all of you, the reality is that lots of people meet at work or through family, so there really isn’t anything unusual or wrong with your having met someone your dad works with.
As long as your boyfriend is not married, or a criminal convict I can’t imagine why your family would be upset, except for the fact that you’ve kept this from them, and even that can be dealt with. It also doesn’t sound like your parents have forbade you from dating or from dating anyone your father works with, so again, I’m just not seeing the problems. In answer to your question, I’d advise that you just make the introduction of the relationship to your family light. Don’t act like there’s some big, dark secret you’ve been keeping from them. Let them know that you’re happily dating someone, who he is, and that you want to share your good news with them. No biggie! 🙂
I definitely wouldn’t advise breaking this off — especially since you haven’t even seen what your family’s reaction will be. So tell them, keep it light, and enjoy yourself! 🙂