I look around at my last 2 work places and have yet to meet more than the occasional mid-40s professional who is in positions of technical ownership. Most of them have moved into positions of management (paper pushers for the most part), architects (whatever that means) or moved out (to whatever it is they do, hopefully something interesting).
Those who did move into management and position involving architecture were not necessarily more technically proficient than those who moved out, with a history of accomplishments that identified them as suitable for those positions. In most cases it was just a case of who one was acquainted with. Put simply the technical field is not a meritocracy beyond a certain watermark.
I have yet to hear a cogent argument on why folks in their late 40s or early 50s are not adequately represented in programming positions start ups or otherwise. What is unique about programming as a practice that make it unsuitable for professional beyond a certain age?
In most professions that have similar age barriers to early exit (sports comes to mind immediately) one case expect to be compensated handsomely for the short while that one has is holding on to the position, this is not the case with programming.
Leaving aside the argument that most programming positions do not require any education because they are no longer "creative" functions just functions of component "assembly" and as such do not require the experience gained from years of practice, what changes does the industry require to undertake to effective use the experience of folks who have worked hard to gain it?
I certainly do not have the answers.