In sci-fi fantasy novels like Star Trek, nanorobots are sometimes presented as a tool for healing people. It is hard for the normal audience to say, if this technology is realistic or not. Will such nanobots ever become realistic, and if so in 10 years, 100 years or 500 years?
Giving an answer is not so complicated as it looks like. At first let us describe something which is in the near future possible, or even today. A step into modern medicine wouldn't start directly with Nanorobots, but with household robots which are helping elderly people. The classical example which is available since many decades is a simple electric wheelchair which allows people to make a ride, even their legs a no longer working. A more advanced form of such a tool would a walking robot, which travels together with the patient. Such a device was shown in the hollywood movie “I, robot (2004)” which is bringing the inhaler to an old lady, but the same sort of technology can be seen in the series “Real humans” in which a household robot is making the lasagna for an older guy. My prediction is, that such helping robots will become commercial available in the next 20 years, perhaps earlier. But from a technical point of view, such technology is realistic and it will improve the situation a little bit.
Nanorobots are a more difficult to evaluate. Right now, there is research ongoing in the direction of DNA Nanorobots. That are machines, not build with metal, but out of DNA and they are tested, if they can repair a body from the inside and measure information. The promise is, that such technology can really improve the medical condition of people and extend the lifespan. But, it is hard to say, if and when a dna nanorobot became realistic. As far as i know, it is mainly a research project without an application. The researcher are working in that direction, because they hope that one day, they will become successful. DNA Nanorobots can be called the most advanced form of robotics, because they are not simply a mechanical tool like an autonomous car or an automatic wheelchair, but the idea is bring medicine forward.
As a summary, we can say that today well known medical devices like an electronic wheelchair is a product, which is available. WIth a horizon of 20 years, walking robot which can help elderly people will become available and beyond this horizon DNA nanorobots are an option for further development.