The basis for an all-ages rating is something an elementary school student could view together with their parents.
Although it depends on the content of the entire product, a product with depictions of nudity as the main subject would be classified as R, and a product with sexual depictions would be classified as for-adults only.
Please be aware that if your product features depictions of female genitalia or nipples, including those covered by fabric/cloth, it will not be possible to register it as all-ages.