I am trying to identify a book (or series) that I remember enjoying very much years ago. Probably in the 1980's or 90's.
One of those "crowded earth" type of societies, with big (underground?) cities and a carefully controlled society (reminds me of the Cities in Asimov's Robot series). People were only allowed to have a certain number of children, but many exceeded that and the kids were called "illegals". Such kids were not registered and didn't get rations, so they grow up underfed and street-smart, and some are "sold". If illegals are caught, they get registered and can live normally but with some limitations (can't reproduce).
There are some people with psi talents who are educated separately. They were called "Talented" (capital T).
One main story protagonist was an illegal girl who is discovered as being Talented.
One scene I remember clearly -- a Talented boy succeeds in controlling the takeoff (landing?) of a plane that just had to get off the ground but there was some reason (weather?) why it couldn't fly normally. Someone asked "where'd he learn to fly planes?" and someone answered that all boys relate to flying planes, or something like that.
Another few scenes: The illegal protagonist frees a group of kidnapped or sold children from some guarded and locked holding room on the industrial or storage levels.
The illegal protagonist gets to eat a real fruit or vegetable once an a while. In one scene she enjoys something crisp -- I think a pepper.
She is afraid of the people who find her when looking for Talent, but she ends up going with her. She is taken to someplace much more spacious and luxurious than she has ever seen. She is shown to a large private bathroom. She washes hands, face, neck, anything that is exposed before rejoining her "captors". Someone says or thinks that she should get points for nonchalance.
She meets there an older woman who had let her hair stay gray. The protagonist is surprised. The woman says something about having promised her husband she would grow old gracefully.