In the State of NY, an individual turns 18 years old, that individual is responsible for their decision making when it pertains to their personal matters, finances or health related decisions.  He or she is now responsible for themselves and has the sole responsibility to make their  life impacting decisions.  

However, for adults who are unable to make decisions for themselves such as an individual as an adult who is developmentally disabled or a handicapped adult, one can ask the Courts to appoint a guardian for that individual.  

Guardianship is a legal relationship which is created when a person or institution named in a will or assigned by the court to take care of minor children or incompetent adults.  The term "guardian" may also refer to someone who is appointed to care for and/or handle the affairs of a person who is incompetent or incapable of administering his/her affairs.  

In New York State, Family Court, Supreme Court or Surrogate's Court are responsible for guardianship cases depending on the type and the individual requesting guardianship.