Is my boyfriend hiding me?

Julia

I’ll try to make this as summarised as I can. Ive been getting feeling that my (20) boyfriend (39) is trying to hide me from his family. We’ve been dating for almost a year now and we haven’t met each others families. My parents know about him but I don’t live with them so the conversation of them meeting him rarely comes up. However I’m 80% sure his family knows nothing about me. And yes I’m 100% sure he doesn’t secretly have a wife and kids, we spend too much time together for that to be the case. I’ve invited him multiple times to family gatherings but he’s always declined. He even passed on a family birthday party for me, which I thought would be a good time to introduce him to everyone. He never invited me to anything that involves his relatives. It’s starting to feel weird at this point and it makes me uncomfortable. Is it the age gap? I don’t know what to do