Hmm

I imagine it’s not that much, riku said he’s only a bit older and he’s just arashi’s uncle so he could be the dads younger brother, plus I don’t think he actually owns the shop, I think he’s just helping out while they’re gone (I mean to say he’s not like middle aged or anything even though that’s not the most reliable inference ever)

Around a 5 - 10 year age gap give or take.

Yup