I feel like this series aint gonna go the Usagi Drop route. Honestly, when it started I thought that Aina's mom was gonna be the love interest, before it turned out to be (looking like) the mayor, or at the very least not Aina's mom (who disappeared for the most part).
I wouldn't be surprised at all if Aina ended up having a thing for Shirou, but there's nothing in the series that really leads me to believe Shirou would ever reciprocate, or that the series would make it weird. Aina's just there for CGDCT factor, not to be part of a harem or whatever.
I don't really feel like the fairy+guy age gap is a big deal considering so many series with elves have the exact same situation going on, the "younger" guy's still a fully-fledged human adult, it's fine imo.