There are various ways a person will be able to live beyond 100, 200, or maybe even 1000 thanks to medical trechnology in the future. Eating and drinking the right things for the body and even not eating can help people live to be over 100. But there is a genetic limit to how old a person can become. The telamerase molecule on the DNA determines how many times a cell can replicate. Once it is removed and replaced by another molecule that can be replicated, in theory a person could live forever. Each copy of a cell would be an exact duplicate.
In the future, nearly every baby born will have a sample of his or her DNA kept on file for future reference. If there is as genetic disorder, doctors will be able to correct it by seeing which gene or genes caused the problem. Gene replacement could correct the problems and will in the future allow doctors to reverse the aging process so that people will be able to stay at their optimum age for the rest of their lives. That means a person won't need to retire at 65 or 70. Once he has enough money saved and invested to live on for the rest of his life, he could retire then. That might be when he is 200 years old. Then if he runs out of money after, say, 500 years, he could get another job and work for another 200 years.
Biosynthetic organs and systems will be implanted to allow people to live indefinitely. A synthetic heart that uses the body's energy, a nuclear battery, and a chemical catalyst that will convert substances in the blood into energy will replace the natural heart and use an electrochemical system in the muscles to expand and contract them. The heart may run flawlessly for centuries. A chemical catalyst will be used to help the liver and will work better than the liver. It will be faster and more efficient. Even the arificial kidney which will work like the natural organ will be implanted to help those with kidney problems to live longer healthier lives.
Those who live for centuries will need to download memories into computers. They will first have brain implants that will store more information than the brain can store. But after living for maybe 300 years, they may feel their brains are a bit full and they may want to make room for more memories. Downloading certain memories and having easy access to them may be as easy as allowing a compuer to collect them and keep them. Duplicate memories or bad memories a person would rather forget could be eliminated in the same way computers make room on hard drives.
Diseases will be prevented by nanobots, bacterial and viral delivery systems, the synthetic organs, and a synthetic immune system that will assist the existing one. Body programming will allow people to program their bodies to eliminate fat and other things that aren't wanted. That means a person might eat like a horse and be slimmer than a colt.
Living beyond 100 is hard to do now. But living well into the triple digits or even the quadruple digits will be possible thanks to advanced medical technology in the future that will reconstruct the body to make it the best it can be.