I think it also depends on how you define "worse". I've had bad times in my life, but they were all bad in different ways, and my mental state during those times varied as well. So it's basically impossible to compare them to each other and say which one was "the worst". Like, for example, certain times in my life that were really awful from a logical standpoint (crappy job, no money, no friends, whatever) were times when I really had myself together mentally and could gracefully weather that rough patch and see myself through to the other side. And then there were times when my life didn't really look all that bad from a logical standpoint, but my mental health was a mess and I was just a disaster and I remember being very miserable.
With that perspective, I find it easier to be optimistic about the future. Because presumably, the older you get, the more you get to know yourself and the more time you have to improve your mental health issues. So while life itself may or may not get better or worse, *you* get more able to handle whatever happens.