I think a serious problem here is that he thought he was free from the treadmill, but it wasn't true. He just so happened to be at a certain rung of the ladder

I think a serious problem here is that he thought he was free from the treadmill, but it wasn't true. He just so happened to be at a certain rung of the ladder along with all of his peers and as he retired, it felt like he climbed even further and had "made it" in a way they hadn't. But he had really hit the pause button on his accomplishments, so as his peers entered the next life phase of increased career security and financial options, he was left behind and suddenly found himself low on the ladder looking up. Much of his personal angst came from this.