The assumption of ageism in Silicon Valley, that is as people in the technical field gets older, their capability decline relative to young people, making them less competitive in the job market, seems to be rather prevalent. As an middle age programmer myself, I find this notion very wrong. The knowledge and capacity for older people to learn are seriously underestimated. Specifically I repost my response to an article in IEEE Spectrum rebut the concept of half-life of knowledge
I am rather skeptic about the model of "half-life of knowledge". The idea is some knowledge expires after a period. It becomes useless. The effort in acquiring the knowledge will be nullified after the expiry date. This manifest into the phenomenon that old engineer becomes less desirable than young engineer. The author assume this model is self evident and has not bother to provide much evidence to back it up. I would say the burden of the prove is on the author. I am not convinced that "half-life of knowledge" model really explains the reality.
First consider mathematics. Most of the mathematics knowledge we use are well over 100 years old. I don't see any evidenced that mathematics knowledge are expiring. Arithmetics is the same. Calculus is still useful. Logic hasn't changed. I don't believe people can be exceptional engineers without mastering these 'old' math.
Being a software person, I consider algorithm and data structure foundational. Again I see no evidence of them being irrelevant. To program HTML DOM, you need to understand the data structure of 'tree', how it is structured and how to address and traverse them. To process big data, it is not enough to setup a Hadoop cluster. You need to understand the concept of computational complexity and why no amount of hardware can be fast enough if you problem's complexity grow at a rate of O(n^2). Again I see no evidence of these foundational knowledge are expired. Rather I think the have become more relevant ever.
What about software? The Unix system that power so many devices today is four decades old. The BASH scripting I wish it would dies because it is so antique and cryptic. Instead we are still building new software with BASH these days. Some work horse programming language, like Java, is a 'young' programming language only about 20 years old. But it is merely a descendant from the older languages like C and C++, which in turned come from the similar programming paradigm that date back to the early days of computing.
I find the "half-life of knowledge" model dubious. It is true applications change rapidly. But these change are only superficial. New knowledge are build on top of old knowledge, not replacing them. Foundational knowledge are as relevant as ever. They are not expiring anytime soon.
Turn out one of the best repudiation is in a question and answer in Quora. A poster asked, in a blunt language, for What do people in Silicon Valley plan to do once they hit 35 and are officially over the hill?
The presumption is so patently wrong that it draws a long list Silicon Valley luminaries to directly contradict the poster by recounting their own mid-career progress and achievement. Their evidence are overwhelming. To portrait Silicon Valley as young people's playground is just delusional.