As an older developer who has been developing for more than 20 years, I find that the reason for the "half-life" to be the impedance mismatch between the demands of a family and the demands of mismanagers (and their crunch time and death marches).
Eventually, developers start saying things like "I want to watch my kids ball game" instead of being at the office and dealing with the latest manager-inflicted crisis. 60 hour weeks are not family-friendly, and the developers that choose family over the office end up getting pushed out the door.
Yeah, as someone who will be moving into the 'married & family' stage in the next few years, I am getting concerned about the paces I will be expected to put in. I am not going to be working until 11 at night on my kid's big event. I'm going to be there for my kid.
Eventually, developers start saying things like "I want to watch my kids ball game" instead of being at the office and dealing with the latest manager-inflicted crisis. 60 hour weeks are not family-friendly, and the developers that choose family over the office end up getting pushed out the door.