I'm 65, and I would say the idea of suicide as a real option opened up sometime in my 50s because it became so very clear that I'd lost most of my life and no longer had decades ahead of me to try to get well. The idea of suicide as a theory probably opened up for me around the age of 13, but it was just some vague notion. On some TV program in childhood, I recall hearing a psychiatrist make a comment that has stayed with me throughout my life, and I so wish I could find literature related to his view. He simply said that "a young person can die spiritually, and that is why it is so critical to help them before it's too late." I do think it's possible to die or almost die in terms of spirit but just keep on trucking as if you are fully present and engaged in the world before you. I sort of feel that I've been a ghost since 13, though there has always been just a tiny bubble of life within.
To answer your question about the value of hanging on: some small spark of life remained in me and with that, I have fought very hard from 20s on to recover and thrive. I have explored just about everything, and my experience is that not much worked. There has been some improvement, mostly from breath and body work. Talk therapy never helped or meditation or New Thought/Religion. Somehow, I'm still at it. I was due to begin grad school online at Harvard this semester but dropped out two days before class began due to depression. I'm going to try again for the Fall, or I hope I will. I just committed a lot of money to start a new business, but today has been a bad day, leading me to this site, and I'm wondering if the man I made the commitment to really would follow through and sue me if I don't pay on the agreed upon date. If I'm dead or moving in that direction, who cares anyway? I suppose I'm reaching a point where it won't matter because Nature might just take her course. So...I cannot say there is value in hanging on unless your death might set up terrible trauma for loved ones.
I have joked with friends about the cliche: "Life begins at 30, 40, 50," etc., because I'm still waiting for that time to happen. As hard as my life was in my earlier years, it hit like a hammer just after I turned 40. Every decade has been more painful, with more drama and hardship than the decade before. I cannot, for the life of me, tell you why. I am a gentle librarian type, vegetarian, animal lover, wanderer, highly educated, kind, sensitive, nurturing, and most people see me as calm and grounded, except the few who have really gotten to know me. Ironically, I make a living as a life coach. It works because I have so much book learning to share. Based on my life and the lives of friends my age, I'd have to say that it does not get easier. I have had one friend who suffered a great deal in her 20s/30s, and in her 40s she entered talk therapy for 15+ years and she created a healthy, rather happy experience that has lasted. She was a practical person, not a seeker, not highly sensitive, and she was someone willing to settle in life. I think that makes a difference. She is the only success story I know of.
There is a brilliant book written by psychologist Alice Miller entitled The Drama of the Gifted Child. Miller explains that pretty much everything that can possibly affect us and screw with us happens during infancy and toddler years...and we are usually not going to get over it. Generally, in other words, toxic mothers (or perhaps well-meaning but immature/ignorant). I'd also like to just throw in an aside that I'm astonished girls and women are freely allowed to procreate as much as they want, but that's another conversation. I'll finish with the cliche that you never know what's just around the corner. I haven't found anything wondrous around the corner or even slightly encouraging. Life just goes on, and maybe that's OK. My animals have been, for the most part, the reason I've stayed alive since around 2005.
I did not struggle with suicide until much later in life. Not in my teens or twenties, though I was desperately unhappy. I did ponder it but I really wanted to get well if I could and I did a lot of work on myself. What I've discovered, just my experience, is that we can't really know what is going on. Our minds cannot fathom reality. Maybe we can pick up some pointers that might help us want to stick around in case life gets better. That's what happened for me, just holding onto threads. Hope this answers some of your questions with as little TMI as possible.