My theory is age plays a major factor in hiring these days.
When the government can stipulate a requirement for certain jobs that you have to be under 35 to apply I think private industry secretly follows suit. Thackney disagrees with me on this but it is what I have found to be emperically true in my case.
I am not trying to say that doesn't happen, or doesn't happen at most place.
But it has not been my experience. I work in consulting/design/construction engineering and design for the oil/gas/petrochem. Knowledge and experience count for a huge amount; mistakes are hugely expensive.
Good Judgement comes from Experience.
Experience comes from Bad Judgement.