If a boomer retires, he leaves the labor market true. Wouldn't it make sense that a job opening was created by his leaving the workforce? Not in all cases surely, but some of these people open advancements for others, leaving their jobs open. Eventually there should be a replacement down the chain after people advance.
We are at the beginning stages of boomers retiring, there will be millions over the next decade. If that is millions of jobs lost as well, we are doing something terribly wrong. When a teacher retires, do we close his class or hire a new teacher?