It really depend on the health status of the women, different people age at different rate. People who age slower, can afford to have children at an older age, while those who age at a faster rate, would be vise verse.
As somebody whose mum is one of those ageless women, I know for a fact, people who age slower, it might be safe, to give birth, well into their late 40s, but for some other people who age slower, reaching mid to late 30s might be a bit too old.
(Just want to clarify, those ageless women u see, the deal is, every person mature and age at different rate, the idea of animals mature at different rate and age at different rate, is not only between different species, but it is also the same case amount the sames species. Only in cross species the gap is very big, when it is the same species, the gap is usually much smaller, even amount human from different part of the world, they mature and age at different speed for example, some India people can still going through their final teenage growth spurge in their early 20s, I have at least 3 India friend, that is like that. Asian people tends to age slower then western people, in adulthood etc. And within people living in the same region, once again, different people mature and age at different rate. These aging relating stuff, is first determine by ur DNA, although secondly, maintaining a healthy life style, could also help u to age slower. Those ageless women u see and hear of, are generally people who successfully age slower, by having DNA advantage and a healthier life style)