Samples are mature women and men (or equivalents from other races). Scanner shows their age, which can easily be in their 40s (it seems to be just a random number from 18 to 50 or something, unrelated to their looks).
There is a variety of body types, so if you're into more curvy ones, they are available.
We are not provided any data as to whether they already have children, and the game does not feature any of them giving birth. There is some talk about including breeding in the game, but the author is not Japanese enough to include children in training, so it would require jumping through a few hoops.
Haven't played this game before, is there any actual (robot) sex or is it just BDSM and tentacles?
Yes, you can prostitute your samples to humans and a robot merchant. You can also involve male samples in training your female samples.
No, the player character does not have sex, and doesn't seem to want to do so. At least, he refused when the robot merchant suggested installing the equipment directly on him.
Wait a minute... This is just cuck porn with extra steps! >:0
Since the player robot is not in a personal relationship with the samples, I do not think "cuck" is the right term. I think player robot just likes to watch.