Just a heads up: Even with a good and patient partner, first-time gay sex experiences tend to not be great, especially for guys who want to bottom. Being direct and honest with your sex partners is likelier, I believe, to result in an enjoyable first time. People with no experience are no more virtuous and certainly no less desirable than those with lots of experience.
There’s no degree of sexual experience that is shameful or embarrassing. In sex, as in life, I always maintain that the best policy is honesty. That’s not as much of a turn-off as you might think it is. I still think the best course is to be honest with potential sex partners and tell them you’re new. Good sex partners are hard to come by, and beginners have to be choosy - there are bad people everywhere who would use your lack of knowledge against you. That said, I know it can be hard to find such a sex partner.
So naturally, I’d encourage you to have that dialogue with the person you want to explore sex with for the first time. His experience and advice were helpful, and I can’t imagine bottoming for the first time and experiencing those things - exactly as he said I would - without his guidance and understanding. He was several years older than me and was able to teach me a little bit about sex - and, most importantly, he was able to prepare me for the trials of bottoming (namely, that I would make a mess, there would be poop, and that bottoming would hurt at first). In my first sexual experience, I told the guy I was a virgin.