SuttaCentral
Due to modern medicine advancement, people can be hooked up to life extension machines and live much longer than 50 or 100 years ago.
Is advising people that one doesn’t need to do this a form of killing?
No. 3 and 5 would be the part open to discussion.
No, they are two different things. Someone facing terminal illness at the end of life does not commit self-killing by signing a legal document asking that no CPR be used. The terminal illness is the killer, not the person. 
First start off by thinking how traumatic the death of that person would be for the person. Some illnesses are very painful to die from. Starvation is very hurtful as well. So, taking that into account, concern with the fact whether a prolonged life is less or more suffering. Maybe also they can be cured, do a 180, miracles do happen. The purpose is life, not death. Then also the most important part: understand the value of human life. It is priceless, a matchless gift that may not be found in a trillion next births for that being. Maybe giving them as much Metta and Compassion in that human state far, far outweighs death. Wouldn’t it?
The issue is not the merits or demerits of life extension tech. The issue is precepts wise.
People have their own circumstances to decide for themselves. Most importantly, we want to avoid situations where kids asked the doctors to removed already hooked up life extension machine to their parents because they all run out of money, and thus the kids commit heavy evil kamma of killing parents.
As monastics, if we can advise people that they don’t need to be hooked up in the first place, it can save some people from having that moral dilemma down the road.
I just got an answer from my teacher that says not hooking up to the machine is not killing. Because no intention to kill, just no intention to extend one’s life. We are not advising them to die earlier, just not to extend their life. But if they are already connected to a machine that sustains their life, then cannot ask them to remove or else it is killing.
It is a very difficult question with very many views points, and your teacher must be very wise. And the most important decisions made right are often the most difficult ones to make. In difficult decisions, sometimes the easy route isn’t the correct one, and ends up being hard in the end, and the hard route ends up being the correct one, easing up the situation and it’s stress in the end. However, every situation is unique, so that’s why we are Buddhists, for the purpose of Right View we can learn to make the right and correct decisions on the way to ours and others Nibbana and Liberation from suffering to meet the correct End for ourselves and others. We know every life matters.