Even though Eriu species can live as much as we do, the life expectancy during pre-dynastic period is around 50 years old. The infant death rate is low, but still a problem. Even though, as you will be able to read, Eriu inhabitants have a pretty good knowledge of anatomy and a remarkably good level of hygiene, there were some types of illness they couldn't understand/heal, and, unfortunately, pregnancy too wasn't 100% safe, but you can consider their health level very good, especially if compared with other ancient societies of our world.
Hygiene
Generally speaking, Eriu inhabitants have a great level of hygiene, which helps them being generally healthy. Not only they wash themselves frequently, but they also take care of their teeth, usually using bicarbonate and salt, and adding some plants, like mint, to give it a better taste. They also produce soap with some of fatty oils and fats, with alkali. For washing their hair, they basically mix soap with water, and add some herbs to give more glean to it, or use ashes of some plants, plus coconut oil, because the ashes would leave the hair too dry. Having a great system of sewers also helps keep a good level of health.
Anatomy knowledge
Eriu inhabitants have a good knowledge of the "human" anatomy, since there is no taboo about dissection. They know that the heart pumps the blood into every part of the body, for example, but some other organs are more "mysterious" for them. For example, they don't have a very clear idea of the function of the kidneys, and they believe some other fluids too, like sweat, are pumped by the heart. Another interesting organ for them is the brain: in Eriu, the heart is considered the center of the knowledge and of the intellect, but they noticed that damages to the brain can cause problems to other parts of the body, such as the arts, so the brain it's considered, alongside with the spine (even if they don't see the connection between the two of them), the center of the movement.
Medicine and doctors.
The greatest part of their medicines are based on plants and minerals, but medicine is highly connected with religion. Even though Slainte, goddess of Medicine, will come to life later in Eriu history, people pray already to this nameless deity. She exists, in some ways, because people need her. Doctors are usually temple members, or, if they come from a culture that doesn't have true temples, like Icryses they devote themselves to help others, like Orudel witches; they usually specialize themselves, so you'll have dentists, orthopedics, obstetricians, and so on. They know how to create and use disinfectants, anti-inflammatory, and analgesics. In Eriu, the mental health of the subject is also considered very important: in fact, they know the existence of the "depression", and they treat it as other illness.
Transitioning methods
As already stated (see Love, sex and Marriage), transgender people are accepted as they are, but if people still decide to transition, there are mostly two ways: -Surgery: The removal (testicles) or implants (breasts) of some anatomical part is possible, mostly thanks to ---, a famous surgeon who revolutionized surgery in Eriu's history, even in its early stages. Genitalia, however, can be risky, and the science is still making progress about them. -Rún's secret potion: The god of secrets Rún knows the existence of Slainte and can actually speak to her, and she told him how to prepare a potion that will make people change gender. The difference between the two methods, is that the potion will make all the body change, while with the surgery people can just change some aspects of themselves.