That's a false equivalency. They're more likely discriminating between a 25 year old with 3 years of experience, and a 50 year old with 20 years of experience.

Is there any evidence that companies discriminate between two people with exactly the same experience over the last 5 years, with one having additional 20 in something else ?

I'd be surprised if the average 50yo applicant seeking a development job was a second-career "washout" (whatever the word washout means for someone who actually has managed to stay working in any career for a decade). In fact, I'd guess that among 50yo applicants, more of them were teen hackers and have 30+ years of software development experience than have <10 years of experience, though perhaps the median might be more like 20+.

They had another career before this which means they WANTED to go into tech. I feel like the chances they would be more passionate and dedicated are much higher.