Eligibility for Euthanasia

Question: What conditions, if any, must a person satisfy in order to be considered eligible for euthanasia?

When thinking abstractly about euthanasia, most people tend to associate it with someone who is in serious pain caused by, or related to, a terminal illness and thereby wants to remove their life support. When someone someone associates this sort of patient with euthanasia are they implying that these are the necessary or sufficient conditions for candidacy for euthanasia? Well, I hope not.

Euthanasia should be a legal option for everybody who wants it. Of course, if where authorized for every person who wants it at any point in their lives, there would be an obscene number of people who euthanized themselves due to minor problems which caused them to act/think irrationally (imagine the emotionally unstable teen after a break-up, or the parent who threatens to euthanize themselves if their child doesn't 'quit being a homosexual').

There should be a few steps and considerations made before a person becomes eligible for euthanasia. I think  that there should be a waiting period (probably no more than several months), during which a person can reconsider their decision and consult with a number of psychologists. The length of the waiting period and the number of concurring psychologists required should be adjusted per the person's age/anticipated (adjusted) life expectancy, and the pain/suffering that they feel. In general, the amount of pain.suffering a person is going through should have a negative correlation with the waiting period and number of psychological evaluations, meaning that more pain equates to smaller waiting period and less evaluations required. Conversely, the correlation between life expectancy and the waiting period and number of evaluations should be positive, in that a longer expectancy should equate to a longer wait and more psychological evaluations. Though the pain should have a heavier weight due to the fact that a person could very well end up living fifty years in terrible pain.