Miles’ Ability
Simple theory really, just had a thought that maybe Miles’s ability comes from being born on the Island where the spirits of the dead who can’t move on seem to linger – perhaps also affected by both his child self and adult self existing in the same timeline? (On a side note I recall him acting weird around Claire after her house exploded but she escaped unscathed, as if she was actually dead…? And MIB bought her back…but why?)
As to why Hurley can see dead people too…who knows. Maybe his craziness opened his mind up to all sorts of possibilities?
Don’t people say that young children (reeeally young) can see ghosts more than others because their minds havent adjusted to whats physically there and what isnt.
Maybe that explains why Miles can talk to the dead.
Like you said about adult him being around younger him, maybe younger him just didnt grow out of it because Miles was physically real.
As for Hurley, we dont know if he could see ghosts from a young age or just from the mental hospital. If the latter then yeahh im gonna have to agree with you and say his mental stability opened up his mind to new things – ghosts haha