You can help them accept your boyfriend by having plenty of reasons of why you love him and why you’re good together. You’ll need to be prepared to answer whatever questions they have, like where you met, how serious you are, and… why he isn’t dating someone his own age. The key is not to be overly defensive. If you are, it gives the appearance that you’re aren’t secure in the relationship or your choice in a boyfriend. If things are really as genuine and happy between you as you say they are, then let the relationship speak for itself, answer any questions honestly and openly, and accept that not everyone — including your parents — are going to accept that a 30-year-old man has good intentions when dating an 18-year-old girl.
If your parents are willing to meet him, you can introduce them so they can see for themselves what he’s like. If you are financially independent, you really don’t need their approval (although it would be nice). If they still support you, you need to respect whatever rules they might have. You’re old enough that hopefully you’ll be on your own soon and you can do whatever you want.
Do be careful, though. While your age difference isn’t necessarily “taboo,” it is big enough that it could potentially cause a lot of problems. There’s a reason why 12-year age gaps become less of a “thing” as people mature but remain rather shocking between people a teenager and a grown adult. You don’t have the life experience your boyfriend does and that puts you at risk for being taken advantage of. Be smart and proceed with caution.