For how long have you been feeling like this?

Yeah, I think my trajectory is like yours except it didn’t begin that early, first vivid grey memories from 13/14 yrs age. But one incident is a bit similar to you staring at the sky – I had bunked school after lunch and wandered into the countryside (school was at the outskirts of the city I lived in). I still hear the dull hum of distant highway trailers that was like a solemn soundtrack of my schooldays. I got near a sandy racing track where they were go-karting. I’d never seen those before, so I dropped my schoolbag and sat upon a big boulder. Just sat there on a hot afternoon for about two hours- almost one and half hour after the go-karters had left. Without any reason, except for clouds passing slowing overhead. It wasn’t grey but I recall a depressing yellowness all around. I recall first stings of humiliation in that moment of realizing my natural aloofness, kind of predicting a pointless, desertlike life awaiting at the end of childhood.
I didn’t face any major traumatic event either. And I guess that’s worse because then I have no justification for being dead inside :/