Mid-60s being old is personal opinion from what I can tell (long way off for me) by talking to various relatives /friends. My uncle died aged 63 and my Dad has lost several friends between 60 and 70 and plans to retire asap. However, some people keep pushing on and working way past this.
Maybe he wasn't actually that interested in keeping going, even with it being the highest level he's done before. He did it and can tick it off, maybe that's enough for him. I could push a lot higher where I work but have literally zero interest in it. Everyone is different and we've seen nothing to confirm anything malevolent happened.