I guess it's probably not possible for everyone, but you never know.
When I was in my early teens the idea occurred to me and, being ceaselessly curious about everything, I was determined to have a go.
It became clear quite quickly I wasn't anywhere near flexible enough, so I settled on a position that got me closest and worked on stretching for a while, probably a few weeks (this is a while ago now though!). The position I used was to lie on my bed (which has no headboard and a wall at that end) with my head up to the wall, I'd then lift by legs and torso up so I had my head on my pillow and the rest of my arching upwards, so that the centre of gravity was about above where my neck and head were, so that with a bit of support on my back from my hands and my feet resting against the wall above me, I was quite stable. In just this position your back is mostly straight, so your cock is still a fair way from your mouth. It was mostly a case of adjusting the centre of gravity to be further away from the wall edging my feet down.
Fairly quickly I could pull my foreskin out a bit and lick that and after a little while I could lick and suck the head of my cock. I wasn't able to suck myself to orgasm, I think mostly because the position didn't allow room for much movement, so I was doing all the work with my tongue and getting tired and uncomfortable and having to finish with my hands, which actually was really erotic because I was seeing it from a totally new angle :-)
I stopped doing it quite quickly though because, despite the cool view, it wasn't comfy and I found it was best to uncurl out of the position very slowly so my spine didn't pull anything, so it meant if I was going to cum, I had to do it in that position, which meant either busting a nut into my mouth or spraying it over my face/hair and, while the former was fun, it wasn't really something I enjoyed regularly, and the latter was just a pain to clean up, since I inevitably was doing this really late at night ;-)
So, if you're young and flexible, I'd say have a go, but don't push your luck and probably try and get someone else to do it for you ;-)