So,

I happened to wander to place where the shrine of Boethiah is, a place of a cult of some sort. I was at level 27 or something, below 30 at least. The place is empty, just full of burned corpses etc.

I read somewhere that you must be level 30 to initiate quest. Am I screwed or has anyone experienced this same thing? How to initiate the quest? Now Im at level 34 and just did the quest House of Horrors. The shrine of Boethiah is still empty when I visit it.

I still need a couple more daedric artifacts to get the Oblivion Walker trophy. I missed the one where you were supposed to eat human flesh... I also read one can only miss one quest if being able to get the trophy. I sure hope I dont need to start a new character for this...

Sometime soon after you hit 30, a Boethiah Cultist should randomly show up and try to kill you... if that hasn't happened, you can find and read the book "Boethia's Calling" in order to trigger it, according to the Wiki anyway...

There's supposedly a copy at Knifepoint Ridge (haven't visited that lately), but there's a copy for sure on a shelf at Septimus Signus' Outpost.

At level 30 some random encounters are with bloodythirsty Boethia's cultists. They carry a book named "Boethia's calling". By reading it, it's possible to initiate the quest.

Either this or, once you reach said level, go directly to the shrine and read this book.

Hmmm... I found the book in Septimus Signus's Outpost, read it and the quest started. But when I return to Boethiah's shrine (now level 40), I assume its the same place where is the sacrificial pillar, nothing happens. The place is still empty, just burned corpses etc. Quest also doesnt advance anywhere. This is sooo annoying because I think this is the last Daedric quest I havent done. I've completed 13 quests and failed one before this. Its damn stupid of Bethesda if they coded quest incompleteable just because you happen to wander somewhere "too soon" like I did here at about level 27!!! Bethesda, if anyone of you reads this, this better be fixed in an update!