What should I do? Advice.

I am 20 years old, and my boyfriend and I have been dating for 8 months now. He's 27. My dad knows him and I believe likes him for the most part. My mom and his mom are very good friends. My mom and other family know about us, but my father. He told his family about me and I've been around his family. He now wants me to finally tell my father. I'm nervous because I don't know his reaction, I don't know if he won't like the age difference or what. I know it is time to finally tell him though. I just don't know what to say.