Why an Adult rating then if your sim falls perfectly into the General rating?
Rules by rating in Second Life:
General:
* All users allowed
* No nudity and no sex
Moderate:
* No underage users allowed
* Public nudity allowed unless the sim owner explicitly says otherwise on in-world signs, private nudity and private sex allowed
Adult:
* No underage users allowed
* Public nudity and public sex allowed
Rules by rating in OpenSim apparently:
General:
* All users allowed because there's no user age verification
* No nudity and no sex
Moderate:
* All users allowed because there's no user age verification
* No nudity and no sex
* Difference to General? idklol^^
Adult:
* All users allowed because there's no user age verification
* No nudity and no sex unless the sim owner says otherwise somewhere (in-world, OSW, grid website, sim website, in their own mind implying that "everybody knows" OpenSim does have the same rules as Second Life without actually letting anyone know)
* Difference to General and Moderate? No child avatars allowed because the sim owner doesn't want kids running around on their sim
See also what I've written here (caution, long):
https://opensimworld.com/post/80103
tl;dr: If you don't want naked avatars on your sim, rate it General. Or Moderate at most, and then put up signs that say that nudity and child avatars aren't allowed.