In episode 5 of season 7, Cersei tells Jaime that she's pregnant. Some have pointed out that this does not seem to fit Maggy the Frog's prophecy, but there is another issue.
In the same season, Cersei says to Jaime, "You think I listened to father for 40 years and learned nothing." This puts her age at roughly forty years old. (The active listening probably did not start from birth, but she may be rounding up the number.)
George R. R. Martin drew a lot of inspiration from the European Middle Ages, so my question is whether there are any medieval examples of women of Cersei's age (or older) who gave birth to a child.