Folks, I don't mean to sound rude, but anyone who thinks that age alone, a simple number, says anything about the person, the traumas, physical and mental illnesses, feelings and despair and pain (which I'm just assuming across the board when you join a forum like this) has not understood that we are all a product of genetics and individual experiences.
What happens to some of us in the early years of a young life can bring them to the exact same point where they don't know how or why they have to go on living as someone significantly older. It's not about age, it's about what has happened to us so far. But that can neither be easily measured nor quantified.
I think your post sums it up: decades of experience are enough.
Whether it's "only" two (where many say they are "children" who have a life ahead of them after all), 5 (in my case it will soon be 5) or 8 decades. The only unacceptable thing for me is people who make the decision to end their existence in an emotionally unstable moment, almost on impulse, who are otherwise stable in their lives. Impulsive suicide attempts should be prevented, people who make a decision for themselves based on their life so far and the things they have been through, who exchange ideas here, network, reflect and realize that it is their choice to live or end their existence, I respect - regardless of their age. Yes, "only 2 decades" can feel like a finally long agony, after 2 decades you are of age and should also have the right to self-determination.
And I know people who are mature and very reflective in their 20s, whereas I also know plenty of "adults" aged 30, 40, 50, (...) who have little life experience and act like children.
Just my humble opinion.