I'be had a funny thought. You know harem manga(whether pure romance or smut) with demi-humans are likely to have things like the 500 year old loli dragon? Imagine a series were the different creatures aged different so you had the loli dragon but she was actually equivocally 5 years old so she was literally a child and not some you(the reader) could lust over. And on the other end of the spectrum there is a species that age faster then humans(the beastfolk) so a 9 year old is of age(and looks and acts it, not like Raphtalia who just looks of age) and the readers feel weird about being attracted to her. The age of consent would be 18 or its equivalent, which would be different depending on the different species as they physically and mentally age at different rates. This post came from being weirded out about a 100+ year old dwarf still obviously being a child even in her own tribe and still getting to say "Well I am over 100 so this is fine."