Another point worth making is that in the original Japanese version the characters most likely really were Black Jack and Pinoko doing a cross-over story with Astroboy.
However the dub presents them as Dr. Roget and his nurse Penny. The producers of the dub obviously wanted to depart from the original context and so "Penny" was not a Whatever you call it sort of embryo. The name escapes my memory.
Anyway as a young boy I personally took Penny's claim to be 21 to mean that she was a female midget. There are some midgets in real life that could still pass for children in appearance and this is probably the context in which the dubbers intended to present her by implication.
Incidentally this is my favourite 80's Astroboy episode.
