You're coming at this from a position of ownership of another human being's life. Granting that you do have the right to determine when a human being is "able" to put an end to his/her own misery is straight-up paternalism. It's power masquerading as protection. Misery can't be quantified in years lived but is instead perceived in the moment. Forcing a 5 or 7-year-old to live against their will because you've decided they "can't really get it" is only you asserting the right to decide what is the level of their tolerance. You don't own their body, you don't carry their mind, and you can't fill up the world they live in every second. If the principle is self-determination, then everyone possesses it otherwise, it's not self-determination whatsoever; it's control and conditional allowance by the powers that be. And that's not morality it's control.
This isn't necessarily my position on it. I was refering to it as something I imagine would be held up in opposition.
Me personally? I just don't know what to think really. On the one hand, I'm genuinely not sure a 4, 5, 6 year old can fully grasp what they would be asking. Do you think they could then?
Would you have a minimum age at all? The moment they can speak, if they seemed keen on dieing, would you grant that? Would you expect parents to?
Can you not see that being abused by bad parents who want rid of their irritating 4 year old? Now darling- tell this nice lady with the injection what you told me last night...
Do you think you can reason with a 4 year old? I can't say I've tried- to be fair. But then, I've heard very young children don't fully grasp what death actually is for a while. Maybe that's patronozing though. I just don't know.
It wasn't intended as a personal objection though. Just something that I think could and would create (understandable I believe) unease.
While I'm all for autonomy and the power to choose, I'm not keen on the 'nembutal for all' stance. I think there do need to be some regulations to prevent impulsive attempts, coercion (murder). Plus, a genuine and fair study on who and when we are able to fully grasp the decision.