I'm not saying we should call him an adult all ready, but Greg stated that he met the Gems when he was 22, and it can be assumed that shortly before Greg lost contact with Marty he impregnated Vidalia with Sour Cream. Theoretically, this would make Sour Cream 22 and not a teenager, which is feasible as one of the writers confirmed that the Cool Kids were a mixed age group. But hey, for all we know Vidalia was pregnant with him four years because she's secretly a Gem and YES I am still holding onto this theory. Not Yellow Diamond, but a Gem is possible.