Having an advance directive and appointing a health care agent is a good idea for everyone over the age of 18. Being too ill or confused to make medical decisions can happen at any age. A health care agent can act on your behalf if you become even temporarily unable to make your own health care decisions (such as might occur if you are under anesthesia or have become comatose because of an accident). In New York State, only the health care agent you appoint has the legal authority to make treatment decisions if you are unable to for yourself.