But it really comes down to "good enough". Companies have some pre-determined pay scale for a new position, and more experienced applicants typically want more pay. Given two candidates, both who look like they might be able to do the job, companies may choose the less experienced (cheaper).
While the younger candidate may provide less overall to the company, the difference may be not only difficult to judge, but it may be impossible to test given that you cannot try both options.
And in terms of design, I would argue that humans are so varied that often even really horrid designs attract business. That's not to say that younger designers make worse designs, but that sometimes practically anything would work; it just might bring in a different audience. The result could be the same in terms of bottom line.
What I've decided at this point in my life is that we older people need to either go build our own companies/opportunities, or just roll with whatever job and find our personal satisfaction outside the office. Or just travel a lot to lower cost countries, work a lot less, and have a lot of fun :).
* s/manage/judge