this is a relatively old post but I'd like to reply.
I think if they have GENUINE reasons to do it that isn't just something that can and will be resolved soon, like a breakup, then they can. I first tried to ctb at 9 years old ( I am now 19 ) but had thoughts since like 7 or 8, probably 8 I don't really remember.
I don't think you should selfishly tell minors to wait until they're 18 to ctb, people can go through hell at any age & ctb may just be one of the only ways to escape it, if not the only one.
of course I don't think actual children should be doing it at all, like 12 or younger. I think if a teen wants to ctb they should exhaust all their options first. but I don't understand people who say to just wait, I feel like that's really insensitive because age doesn't define how much someone can suffer. I've been abused almost all my life which led up to me almost going through with ctb when I was only 9. I don't think minors should just throw away their lives, if they are in an inescapable hell then it's very very understandable. I probably worded most of this wrong, so I'm sorry if anything is hard to understand.