I became curious about my own anatomy somewhere around age 11. I guess there had been some curiosity before that age as well, but along with slowly approaching puberty around age 11-12 that curiosity definitely grew stronger. I don't have an exact memory of when I had a look at my own anus for the very first time, but it was definitely around age 11-12. If I would have to guess, I would say the first times were probably already when I was 11.
I had experienced suppositories at home since I was a young boy, but for a long time I did not think much of it at all. But around age 11 - when the occasional suppository experiences still continued back home - I remember having more feelings of modesty in those situations, and probably due to my slowly approaching puberty those experienced started to feel more embarrassing but also more exciting at the same time.
I guess it was that curiosity, that some afternoon after school when I was home alone, eventually lead me to want to see and explore how did I look like when I was in the position to get a suppository. I remember taking a hand mirror from our bathroom, locking myself in my room, getting naked waist down, and getting on my back on my bend and bending my legs up to take a look. It was definitely a special moment seeing my little pink wrinkled opening for the very first time..
That first experience felt somehow really special, and I remember secretly thinking back to it often, so before long I found myself again naked on my bed, looking at my bottom in a hand mirror. Later on I also evolved to lower a larger wall mirror on the floor, so that it leaned against the wall of my room, so I was able to see my entire intimate area in that large mirror when I was on my back on the carpet. It felt definitely exciting to see myself like that, and from there on it became an irregular part of masturbating, which, however, I of course did only when I was sure there was no-one else home.