Assuming the principle of "My body, my choice", having a terminal illness wouldn't give you the right to die nor would being perfectly fit deny you the right to die. As long as the considered mentally competent, they should be allowed to commit suicide without interference. Presumably, such a right to die would be obtained upon legal majority.
There actually have been cases where nurses were forced to participate in abortion.
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So would you say that people obtain the right to die upon legal majority?