it depends on the author's world but I've come across a few similar stories of vampires who only gain their 'vampirism' when they hit puberty, not uncommon to read something like this.
They mentioned in a previous chapter that he could Consume blood as a child. But something changed i assume puberty and he could no longer absorb what he needed from blood
It was mentioned at the beginning that he only consumed blondie's blood while growing up, but as he got older he couldn't get the same essence from it and started getting it from sex.
So... if he's mixed-race and can't drink blood... only essence from sex... then how the fuck did he get through babyhood and childhood?