For a traditional retiree, I can see the mental health relationship if you focused your whole life on career, and then boom suddenly career is over, and you don't really have anything to get out of bed for.
And I wonder if it is like when you push yourself through stressful moments, only to find your self ill afterwards...ie I would never get sick during university exam period, my body would just conveniently wait until holidays to unleash the cold/flu that it had been holding back. I wonder if years of "I just can't get sick right now" leads to this "peak" in deaths at age 62.