No, it's not.
I've never be in pain, from 14 when I began to assplay with one finger, and it feels so good so I put two, and the neck of small bottles, then three fingers ; all of that are in the physiological range of the anus ability.
I think I began to really dilate at 15 when I noticed that a small increase of the girth gives me a strange feeling of mild burning whitch was wonderful . So at each session, by researching this feeling, I noticed that it needed to increase a little bit more the girth of the object, by pushing the bottle a little further, or adding a finger, so four were needful, then five…
I had no goal, and no idea of what was feasible in this area because it was in the mid sixties (no porn at all), but only by researching this wonderful feeling of stretch, I gave me my first self-fist just before turning 16. Just the hand in a beak of a duck shape in and immediately out ; I was a little scared by what had happened, and thunderstruck by the fact that was without any pain. But it was sooooo good.
So I do it again the next day and the day after and so on, until it was not enough, so biger bottles, and my closed fist, first slowly, then punching…
I'm 73 now, have had many times (but not enough) two woman fists in my ass (I'm straight) and my 10,5 cm diameter plug but I failed to take a bigger one I have whitch is 11,5 cm diameter (because my bones ?) and i can't try no more because with age, the anus have lost his elasticity and, after a session, he starts to look like the one you can see in a vidéo I love, on a site whitch name has 4 lettres including 3 x, name of the video : enormes_grosses_et_gigantesques_chattes_anales ; have a look at 8 mn 30 => 8 mn 45
Take your time, don't rush and you will have a big sloppy hole, without any pain