The article linked, Will surge of older workers take jobs from young? gives sufficient argument against the theory for anyone familiar with reality.

If one wishes to limit "new entry level jobs" to "service" and "sales" jobs where wages are so substandard that only old people who also receive retirment/social security can survive there, it's possible that there's some truth in the idea. For skilled jobs, requiring some education, it generally takes five years for the experienced employees to pass on the "company specific" requriements of a job to achieve "usefulness" by the newby, and ten for the new hire to become as competent as the "teacher" was, - by which time the teacher should have progressed so that they both can move along.

Without an opportunity to "mature into the job," which requires the presence of and assistance from more senior workers, the whole economy is stagnated, and you get nothing but iPods, games, apps, cloud computing, Big Data, CRM, "salesmanship" and the like.

John