Is it normal that my adult boyfriend of 2 years hides me from his parents?

Not normal but there might be a good explaination. The fact that you're still questioning it after two years is worrisome though. Whats he really hiding?

He probably his preventing himself from getting the protective parent conversation. He maybe 30 but they still see him as a child so for him to say she's over now will open a door of negative feelings towards them to you. It would make me mad too but I think he loves you.

Perhaps his parents are Christians or he just can't be bothered answering 10,000 questions about his private life.

His parents know about you so it's not that he's ashamed of you. He just doesn't want to share his sex life with them. We don't all want to publicise our sexual antics.

I would have to say that this is normal.
I can only relate this as it happened to me. My current girlfriend Englishwolfe and I have known each other for five years.
My mother decided to say some really insensitive stuff to me about my girlfriend in an email, and sadly, that email was seen by her. And things escalated from there. My mother and Englishwolfe really did a lot to damage their future relationship.
At that time things with Englishwolfe and I were rough and I had to send her back to her parents so she could finish going to school and getting her education.
My mother's mean comments would come up here and there and increasingly I found myself defending Englishwolfe. Finally, after she got her education she moved back to my state. We met and saw each other in secret for almost six months before my mother knew that Englishwolfe was back in the picture.
Luckily for me, my mother was intelligent enough and mature enough to realize that she had been a bit hard on her and has made great strides to change it.
I think if you have a period of history with this guy, he is likely dealing with a disapproving parent and just wants the topic to change quickly. I understand because I have walked this mile.
It will not last forever, but you might ask him if his mother (Usually is it the mother when it comes to sons and father when it comes to daughters) disapproves of you and your relationship to him. Find out what is going on, offer support and do not push it. Let his mother or father come to you first.

He's hiding something from you

Nope, definitely not normal.