There's no bestiality, that's something I like a lot :) it's safe hahaha.
About the age gap... Well yes, It's maybe about a couple of hundread years gap hahaha.
Beasts apparently live longer than humans and for Leonhart to be already a consolidated king it must mean He's not 'that' young in beast terms. So at least a couple hundread years I'm calculating. Sariphi should be around 15 years, as she was presented as a virgin sacrifice. Usually this kind of sacrifices are made with girls that are becoming women, and the general idea we have of this kind of rituals it's puberty that in this kind of setting (like ancient/medieval style) is appropriate.
Even so, there's no sexually involved scenes (at least until now), so you're safe even there. This is a beautiful wholesome manga so I completely recommend it to you.

all I need to know is whats the two main characters age. And ain’t that beastility