What do I do?

Okay so I'm 17 and I recently started dating this wonderful guy. I just feel good around him and he's the sweetest. Here's the thing, he's 20. And I don't know if that's something bad. I know he's 3 years older, but I really like him. My family isn't too fond of me dating any guy. But my dad and my stepmom are 8 years apart. What are your thoughts?