I'm 47. I got rimmed the first time when I was 14 by a very gentle and considerate pedophile. (Please don't berate pedophile's in response). He soaped and washed my arse first, which felt really weird, especially since I hadn't a clue why he would want to do that. I soon found out. Getting rimmed was even weirder. I felt no sexual enjoyment just a very strange feeling, and I just couldn't understand why anyone would want to lick an arsehole, even if it was well washed. But when he he stuck his tongue inside, where I knew he hadn't washed, I thought he was being really disgusting. I enjoyed being sucked off afterwards though.
When is was 16 I left home to live in London. A 37 year old took it upon himself to teach me about sex. He was extremely versatile and taught me everything he knew, and had me do everything to him that he did to me. Everybody should have the benefit of such a mentor. However, I just could not bring myself to reciprocate rimming, and the thought of kissing him after he rimmed me filled me with revulsion, even though he was a great kisser.
It wasn't until I met my second sex mentor at age 17 that I learned about douching. That changed everything. When I knew that my own arse was clean both inside and out, I could let go of the feelings of disgust. Getting alternately rimmed and kissed became something amazingly intimate and for an hour had me on a the best sexual high I had experienced to date. It was then I tried rimming too, very tentatively, and certainly not sticking my tongue inside. I didn't enjoy the sensation of rimming, but I loved my mentor's response, writhing and moaning. The taste was slightly acidic. I greatly feared any fecal smell, because any hint it would have instantly turn me off. But it was absent, there was just the smell of a clean human body, most agreeable.
I have progressed slowly forward since then, and now I really enjoy rimming not only for the immense pleasure it usually gives my partners, but also because of the wonderful soft velvety feel of a relaxed anus, which really isn't much different from that afforded by a pussy. However I always insist on my partners douching first, and I could still never rim someone after fucking their arse, though I know some gay men actually get off on sucking cum out of a newly fucked arse (felching). I doubt I'll ever cross that barrier fully, even if I were to loose my sense of smell. Sucking cum out of newly fucked vagina, however, is real turn on, especially if it is another man's cum.
With HIV concerns, for the last 10 years I indulge only in external rimming, or I use kitchen plastic cling film as a barrier. This is very effective, and also detracts little from the sensation whether giving or receiving. I would recommend this to any one who like me, has difficulty with their feelings of disgust, as a way to approach rimming.
Having said I cannot bring myself to felch, I have several times actually used cling film to rim the arsehole of a partner whom I fucked with a great big dildo. Those newly fucked arse lips where so engorged, hot and sensitive after 15 minutes of pounding that I couldn't resist doing what 30 years ago would have filled me with revulsion. The sensation was delectable to me, and the moans of pleasure from my partner a further turn on.
I hope this account will encourage those who are curious, confused, or confounded by rimming to perhaps take a step forward. It took me a long time to deal with my cleanliness and disgust issues. They are still there, but they don't prevent me from enjoying rimming any more, I'm glad to say.