<human>: Backstory first I suppose. This is only my second relationship and I am now her sixth. In my case I've only been with an older girl but with her, all her past boyfriends have been older. I'm a senior in HS graduating this year and she's in her first year of college. we know each other through our job and thats how we started seeing each other.

So here's the deal, we were randomly having a conversation and we end up talking about how she's never been with anyone younger and she said she hadn't given much thought about it till now. I told her how this is not much of an age difference and asked her if she really felt like I was younger to her (as I always saw myself more mature then my age group) and she said no. The thing is I know it still bugs her a bit.
So my question is what else, if anything, can I say to reassure her that this isn't a problem.
Also other then this little situation our relationship is going great.

Provide a brief overview of the text.
<bot>: Girlfriend thinks it's weird I'm her first younger boyfriend. What can I say to not make her think it's a problem?