I agree with the PP that said it's not about the numberical age but where you are in life.
I can understand how you are in different places in your life and that can put a strain on a relationship. I have watched my friends go through something similar.
How does he react when you want to go out and have fun with your friends, when he wants to stay home and study? Is he supportive of it? Or does he want you to stay home or hang out quitely with him?
I think that one of the most important things in a relationship is to support the other person and let them continue to be themselves. If you guys are doing ok with doing your own things then I don't see the age as a problem.
When I was 18 I started dating a 27 year old ...

We were 9 years 10 months apart. We dated for over 2 years. He was a Middle School teacher and Assit. Manager at the Gym I worked at. He was my brother's coach the year before. Wierd .. but we had the best relationship. My parents loved him. About 6 months after we met I went back to college 3 hours away (the same school he graduated from 4 years before I started!) Since he lived alone my parents would have him over for dinner every Monday night while I was at school. He would answer the phone when I called home that night!!! However it did end because he was ready to settle down with marriage and I was still in college. Just turned out he wasn't "The One". No other reason. Even then the age wasn't a big deal even though number wise it was huge for that age group. I couldn't even drink yet!!
My DH is 3 years older than me. Our friends, DH's cousin and his girl are 6 years apart. They met only 10 months before he was deployed to Iraq. She is finishing Grad. school right now. He is 30 she is 24. He is now home after being discharged medically. He was wounded and is not incapable of working and she is shouldering the future on her shoulders while he will be a SAHD. They couldn't be happier. The age is NOTHING to them. Though I have to say the amount he has changed and grown in the last 5 years since I first met him is astonishing.
If you are happy and he is happy ... I say the age is nothing. As long as the differences you do have aren't causing a problem.
Introduce him to your parents ... why not?

Good Luck ... Maybe he's the one!