I have a long anecdote, but eventually I turn it into advice:

When I was 18, I dated a 25 year old for a little over a year. I was mature for an 18 year old; I knew myself pretty well. The 7 year gap didn't matter. Now that I'm approaching 25 myself, I have a very different perspective on the relationship.

Back then, I actually wasn't nearly as confident as I thought I was. Even though I still think sex is very important, it isn't as much of a priority as it was. I let his experience guide basically every choice we made, even though I didn't see it that way at the time. I compromised too often, and I told myself that was a good quality. We didn't share the same friends, but that didn't bother me either. And even though I consciously knew that it is really hard to juggle commitments, debt, illness, unexpected events, and never-ending daily chores; I didn't really know how it felt to be the bottom line for my own safety and happiness. When I was 18, I "knew" I would change as I aged, but I didn't realize how much I could change in just a few years, in areas that I thought were fundamental parts of who I was. I didn't know that dating someone for a year is like nothing: now I've dated four people for a year, one for two years+. Even though I feel like I'm with my soulmate now, I have more appreciation for how hard it is to choose someone over and over again. Sometimes depression flares up; both people are worried about their jobs at the same time; school and work keep y'all out late for months on end, while the chores pile up; random shit breaks in your bodies and your houses that you never expected; someone obfuscates for months and then you have to do the hard work of realigning your goals.

I think it's understandable for young people to take on dating older people. You don't know what you don't know. But the reason people think it's weird for older people to date teens is because the older knows the teen lacks perspective.

I don't necessarily condemn the age difference. You can definitely still have a respectful relationship. However, two people with a 30 year gap cannot develop a relationship of equals: because you're just not equals. That comes with advantages and disadvantages, and that's fine.

My parents did not like that boyfriend. They correctly suspected that had I convinced myself we were equals, but in a few years I would think otherwise.

Most 18 year olds have a hard time convincing their parents that they are really serious about any boyfriend they have been seeing for 6 months. In your circumstance, this skepticism will probably be compounded by your different life experiences.

I think the best strategy you could take is to acknowledge their skepticismGood luck telling your parents.