My first time was at 14. I'd been going out with my boyfriend for almost a year. He was 19 and lived about a half hour drive away, so we rarely saw each other during the week. He took my virginity early on, and after that he wanted sex every weekend. I wasn't on the pill then so he had to wear a rubber, and sometimes I'd be on my monthly so he had to make do with me sucking him off. Then one day he said he had forgotten to buy any rubbers. I offered to go down on him but he said we could try it like gays do. I was so in love with him I would have done anything. He wasn't very gentle so it hurt like hell that first time and left me sore afterward, but once the pain had gone I started playing with my ass in the shower. Over a few weeks I learned to relax and could soon get the handle of a brush inside. I practiced with other things too and using different creams as lube. The next time he wanted to fuck me in the ass it was easier and it became a regular thing during my monthly or when he'd "forgotten" to bring a rubber. At 15 I was put on the pill to help with painful periods that were interfering with my schoolwork, but I'd grown to enjoy anal by then and would ask him for it when I was in the mood.
The next day we decided to try anal and I took her from behind as she stood bent over a chair, eventually coming inside while deep in her ass. It was a great experience for both of us.
Our relationship was burning bright -- almost too bright -- and a visit to her the next month revealed that we were actually heading in different directions, and we broke up. That first anal sex experience wound up being one of the last times we had sex (if not the last time.)