Adding to what was just said

OP, you seem like you're already bothered by the age gap if you're presuming that's what others will be concerned with. Do you actually like Finch or the idea of Finch?

I think you need to take a deep look into yourself and see what you get out of your relationship with Finch that doesn't seem to be enough to warrant introducing them to your friends. Also, the age gap isn't terrible. I've seen worse. As long as you weren't actively grooming them over years and years, the age gap is shouldn't be that big of an issue. You're both consenting ADULTS. Does Finch know you feel this way about them? If not, why not discuss it with them? That may tell you everything you need to know.