It isn't unheard of at all, though the odds of genetic damage for the child do go up after 40. My neighbor got pregnant naturally when she was 40. She had already had seven children (I hear that having a lot of kids can push a woman's fertility out in terms of her age). I had my son when I was well past 40 (I used a donor egg, so it's not a parallel situation) and when I was at the hospital, they were all talking about a woman from Rwanda who came in to have something like her 12th child, and she was 56.
I’m 42 with one ovary and one tube and got pregnant naturally and have extreme history of endometriosis. Anything is possible.