I'm 18, my girlfriend is 23. We've known each other for a few years, been together for a few weeks. Sometimes people (a mix of family and acquaintances) will ask questions like "Isn't that a too big age difference?" "Isn't she too old for you?" "Aren't you too young for her?" and so on. Those questions kind of annoy me -- I've heard them several times already, I don't want to have to defend my relationship to other people - that's how it's feeling.
I mostly answered something like "Neither of us minds the age difference, so there isn't a problem." It's a true answer, and polite -- I could also snap at them like "that's our business" but that sounds rude.
But the problem with this answer is that they sometimes respond to the "there's no problem" part with "but you are still studying and she's working!"/"you live in two different worlds" and again it feels like I have to defend the relationship I'm in... as in I have to convince them it's not a bad relationship.
So I'm looking for a better answer to respond to the questions about our age difference. Something that's polite but does not leave room for further discussion. How should I respond?