No, the weird part is that he's raising her as a parent. It's an eccentric idea that a parent would want to marry their child. It doesn't matter if their not related, he's still viewing her as his daughter and therefore have an uneven relationship. They're not on equal social standings with each other which is why it can be seen as incestuous.
To one day go from parent and child then to romantic interest is a turn off for many. It's not like they treat each other as childhood friends or even a false sibling relationship, he literally calls himself her parent.
Obviously the narrative may have a better way of transitioning their relationship as they get older, but the idea itself can be off putting to some, and I can understand that.
But I can also understand how it's easy to reduce the idea based on age alone and go "it's not that bad." But, eeeeehhhhhhh.
I mean the innkeeper is more like her dad then dale, I read somewhere but I can't remember where that the girl never saw dale as a father model in the first place and she thought the innkeeper was more of a father figure while dale was more of a brother or friend I don't know the right word cuz I'm not english, plus I Olso read about the light novel from people talking about it and it seems even when dale learned of her feeling when she was a teen he whouldnt get in a relationship or touch her till she was 18 from what I remember, I mean its pretty obvious she doesn't think of him as a dad cuz she always asks the innkeeper for help witch makes dale jealous, I don't remember what the person wrote in the text but this is most of what I remember if I can remember what the text said I'll type in a message later on
Let's not forget that dale is only 19 years old so if this develop to romance then I'm absolutely fine with this. Plus ain't them cute together?
Also, latina is 8 years old and there's only 11 year gap. Just saying.