I don't think it is black and white. We absolutely do need to draw the line somewhere for pragmatic reasons (as another user mentioned, I wouldn't want a toddler to ctb). I think 18 is a pretty solid age to draw this line for neurobiological reasons, but there will undoubtedly be people who at the age of 18 probably shouldn't be ctb too. But then there are people who at age 18 have probably thought it through and people at age 30 who are too young.
Only you can really decide this, but this is the reason I encourage making as impartial of an assessment as possible. The world outside this forum will inundate you with pro-life rhetoric and those on this forum will inundate you with pro-ctb rhetoric.
Try your best to make your own decision and not let others' values influence you too much, would be my advice. Be wary of the biases on both this forum and offline. I would recommend spending some considerable personal time journaling to write down your feelings, the pros and cons of ctb and your method of choice, as well as planning, researching, etc. I've made a contract with myself to exhaust my options for recovery and spending a minimum of 6 months contemplating the decision to ensure it is not done hastily/in impaired mind.
To avoid premature ctb and ensure a dignified death, I absolutely believe a structured plan and serious introspection is needed, ideally free from the coercive influence of others and the impulsivity that mental illnesses can cause (not that mental illness is an invalid reason to ctb, but ideally you can plan in a frame of mind that is not spontaneously influenced by the illness in a given moment)