Ageism is definitely a thing but its also an interesting strategic advantage. Historically the company with the best mix of experience and energy have been the ones that succeed in the long run. That said, for the first 2 - 5 years of their life a company is pretty much a random series of experiences teaching the employees what they don't know. They have to get to the point where they can actually see that there is a lot to learn and not enough time to learn it before they can value someone who has that experience.

Old engineers are like security enhancements, they seem to cost more than they are worth until you experience an event that would have killed your company if they hadn't been there.