All this talk about contraception makes me say, thank Deity for menopause. That is all.
(I'm also well aware of the fact that a woman can get pregnant even when menopausal.)
Back to the story: My mother had to explain to a (very naive) dog owner that even though her female elkhound was an adult and her male sheltie was only 5 months old, they could find a way. The dog owner didn't listen, and they did find a way. The resulting puppies were so ugly they were adorable. This was back in the era when dogs and cats were neutered at 6 months. One of my female cats came into heat when she was 4.5 months old, but since she was a strictly indoor cat who was living with two other neutered cats, I felt she was safe until I could get her spayed (She did, however, try to get my male cat's attention, but since he was neutered he had no interest whatsoever, except that she was interrupting his nap.)