My very first sexual feelings were associated with my asshole. I must have been two or three, and remember that touching myself down there with the tip of my finger felt absolutely great. However my caregivers (mother and aunts) discouraged it, explaining that it was dirty and full of germs because of poop. I remember understanding the arguments, but continued to enjoy touching myself there anyway.
Soon I tried to insert thin objects (the first was a lollipop stick when I was around five), but had difficulty doing so because the concept of lubricant took time to cross my mind. Eventually I realized that spit would do the trick. I then quickly "graduated" to pencils, pens, and other thin, and appropriately shaped, objects. Then, to not so thin objects.
I must have been eight when I discovered my mother's douche bulb and enema equipment on a high shelf in the bathroom closet. Somehow I knew what they were for, and that was how I discovered the joys of enemas and even larger anal insertions. I soon found out that orgasms, great as they were, took on a higher dimension when anal play was also involved. I've been anal erotic ever since, and I continue to enjoy anal play even more than I did in childhood.
Over the years some of the women in my life enjoyed ass play while others absolutely hated it. Those who liked it did so without reservations (although enemas were an issue with a few); of those who didn't like it, some would occasionally oblige to do the honors on me. But all of them resisted my getting close to their bums, let alone any sort of penetration with fingers or penis or other objects. I'm convinced it's basically because of the "poop issue".