I didn’t have my first anal sex until I was 45 or 46. I got married at 25 and broached the subject with my wife sometime during the first two years but she wasn’t interested at all (don’t get me started).
However, when I had my first affair, my AP specifically asked me if there were any sexual things I hadn’t tried but wanted to try. She wanted to give herself to me in a way no one else ever had. It was the first experience with anal sex for either of us. We went slow and used lots of lube, but I think it was still at least a little bit uncomfortable for her.
I always waited until after I made her come at least twice before moving to anal. Our best time was once when she was lying flat on her stomach and I was on top of her with my hard cock deep inside her tight ass. I reached around and slid my hand between the bed and her thigh. Then I rubbed her clit until she came again while at the same time filling her ass with my hot cum.