Not everyone places importance on "meeting the parents". That's kind of an ancient/fabricated step in a relationship that really doesn't mean anything unless you both have agreed that you think it's an important step for you as a couple.
I don't think this is the right gauge by which to judge your relationship's seriousness level.
Five months is a very, very young relationship. I wouldn't let this get to you. I met my boyfriend's parents after we had been dating a week, just because they happened to be at his house, but we didn't make it into a "thing".
Instead of looking for signs, you should be able to talk to him. If you can't really talk to him about what you like, want, and expect, then your relationship really CAN'T be that serious!
"I wouldn't say that we're especially serious, but I'm confident that we're not interested in/dating other people and at our age (early 30's), you don't just spend this kind of time with someone who isn't pretty important...or could potentially become more so."
I'd say that if you haven't had a talk about being exclusive, you shouldn't assume that you are. There are lots of people in their early 30s or even much older who do spend that much time doing casual dating even knowing that it isn't going to necessarily lead anywhere.
I agree with undercovercrab, "meeting the parents" is something it seems like a lot of the women place importance on but men don't, necessarily. I've read a ton of posts on here where women will list meeting his family as an indication of serious intent on his part and then be surprised when
I think it all depends on he individual.
My last relationship was very intense. I felt rather close to him from early on and it didn't bother me for him to meet my parents. He met my mother in the 3rd week of us dating