If the bullet travels fast enough into the skull before the brain can register pain then there is no difference in experience from assisted suicide to eating a bullet. The only difference is the risk of a botched suicide but outside of that the two things are one and the same.
I use extreme language here not to offend people but to illustrate that they are logically the same thing. If you think euthanasia is humane then so is putting a bullet in your own head. If you think putting a bullet in your own head is extreme, then so is euthanasia. Think logically.
Also I love this idea of age being a marker for maturity and the ability to make your own decisions. If my daughter turns 18 at 12:00pm sharp then at 11:59am she is not mature enough to kill herself. But then one second later when she turns 18 she is now mature enough to kill herself in the same way trump and Elon musk are mature because they are past 18. Makes sense.
I can assure you when I look at this world. Nobody is mature. The right and most mature action isn’t always apparent and people make mistakes all the time. For something like suicide I am happy that there are people who give a shit to intervene.