I'm sorry to hear you have struggled for so long. It does lead me to feel sorrow when someone experiences the incredible and torturous challenges of depression.
What also leads me to feel sorrow is the fact that, as a child, there were people who failed you and throughout your adult life people continued to fail you (including mental health professionals). I believe, with all my heart, that it is not you who has been failing. Now, at 68, you face a time where great support and guidance is again needed. Are there any people worth considering who may be considered successful in the way of guidance and support? You need empowering people around you, not those who will lead you to a sense of failure. For example, is one of your kids that sort of person? If so, perhaps it's worth having a chat with them in the way of support and guidance.
By the way, one of the most impressive titles I've heard in life is 'The 3rd age'. My dad used to attend a variety of programs at his local 'University of the 3rd Age'. Myself, I work in aged care accommodation and wish this form of accommodation was globally renamed '3rd Age Care'. The reason I'm rambling a little about this topic is because aging can feel like a disempowering experience in today's messed up society. I believe the 3rd age should really be about taking the 1st 2 stages, childhood and adulthood, and combining them so there is a mature sense of adventure and recreation (aka re-creation). Care should also be given in regard to how members re-identify themselves. For example, 'Who am I now, without certain friends or family members around me?' Every 3rd age care facility should have deep focus on mind/body/spirit well-being, including access to counselling for those who not only face the challenges that come with aging but the challenges that have never been properly dealt with throughout life. Things are fairly well balanced where I work (re: mind/body/spirit) with a fantastic activities coordinator whose coffee mug reads 'Faye - She who is in charge of fun'. I believe she covers the spirit aspect. Anyhow...
I wish I could throw some magic and miracles your way. I wish I could change the chemistry of depression for you, that chemistry that deprives a person of a sense of happiness and motivation, among other things. I wish I could help you make sense of the pain, make sense of how others have interfered with or not helped you form a positive sense of self.
Love to you Shenpa