Phillip James Plauger is a physicist and nuclear physicist, who wrote only a dozen or so science fiction short stories, mostly in the 1970's, then in 1995 founded Dinkumware, Ltd., a company which supplies Standard C and Standard C++ libraries. The world of information technology has benefitted, but the world of science fiction sadly lost by this career move, judging by this short story.
"Child of All Ages," set in the present day (c. 1975) is about Melissa, who looks about 11 years old, claims to be 14, and was actually born sometime around 460 BC in ancient Athens. Her father was what later ages would call an alchemist, and in his search for the secret of immortality he found a herbal potion that will indeed stave off aging indefinitely. The catch is that it only works on pre-pubescent children, and that entering puberty ends the effectiveness of the medicine.
For obvious reasons, Melissa's parents died long ago: Melissa kept on living. She's semi-immune to disease and can regenerate minor mutiliations (such as losing a finger); she even grows a new set of teeth every couple of centuries. All she needs to keep on living is to take her medicine at regular intervals, and not let anyone kill her.
This has from time to time been difficult for her, as many of the periods through which she has lived have been dangerous ones and a child alone can be very vulnerable. She is however highly intelligent, charming and resourceful, and by the late 20th century has over twenty-four centuries of accumulated wisdom and guile on which to draw to stay alive.
Melissa usually keeps her true nature secret, moving from place to place, foster-family to foster-family, to avoid questions about why she never seems to get any older. Her life can often be lonely. She has found friends, lovers, and even husbands from time to time (in pre-industrial civlizations, people were willing to marry a lot earlier than is deemed decent today), but in time they grow suspicious or die, and she must seek another home.
Her potion does work on other children, and very occasionally she has revealed herself to a friend or lover she especially liked, hoping that they could remain together for a very long time. Inevitably, though, her companion will become discontented with eternal childhood, and choose to grow up, and then die (the story does not make it clear if they then live a normal lifespan or if they die quickly upon hitting puberty). And once again, Melissa is left alone.
From time to time, she tries trusting some adults with the truth, in the hopes that they will accept her and let her live with them and conceal from others her true nature. She tries this with May, a social worker; George, May's historian husband, and George, Sr., May's biochemist father-in-law, in part because she feels that the combination of a social worker, a historian and a biochemist might better understand her than would most normal humans.
The story is about how this works out -- and doesn't.
This is a really beautiful story: sad and sentimental without being saccharine; much like Melissa herself, who is every bit as sweet as her name and every bit as pragmatic and cynical as one would expect of someone who has outlasted whole Toynbeean cycles of Civilization. In her very long life she's known great pleasure, and agonizing pain, and while she does not really trust normal humans any more, she still needs them and is capable of loving them.
She's very much the star of this story, and quite believable both as someone who started out as a very smart child and has now become a personality whose accumulated experience makes her not entirely human by our psychological definitions, but is in no way a monster. She's both superhuman, and yet deep down a lonely little girl, and it's impossible not to love her.
Which is, of course, one of her most potent tools for survival.
"A Child of All Ages" was nominated for a Nebula in 1975 and a Hugo in 1976, and re-reading it I can see why. It is a great character story, while at the same time being great science fiction.