What is the worst form of ageism at tech companies in Silicon Valley?

Refusal to hire/consider for hiring people over 50.

Not familiar, I imagine anyone over 50 is considered ancient. I am 67 and still a very productive employee for my non profit.

lack of promotional opportunites or continued training. They dont invest the money any more

That there are plenty of entrepreneurs who think that employing younger employees is better for the company. Sure, they can work more hours as they don't have much of a life outside work with wife and family but in contrast a vast amount of knowledge accumulated during years of work is wasted and a lot of mistakes can be avoided and more efficient production of goods and services can be generated. Something even worse that can be searched for is 40 year olds (and supposedly even younger) go to plastic surgeons to make them look younger than they are.

I have not experienced this, so I will not comment

I don't believe it is ageism if you can no longer keep up, or you can't keep your views & hate of "others," out of the workplace, it is time for you to move on.

Age discrimination by arrogant young workforce.