Age-related words has been used to describe status in a hierarchy for a very long time. It's an euphemism. "The Council of Elders" sounds much better than "The Council of Rich & Powerful". This tradition is in fact much older than most of our words so it's pointless to argue about its semantics. It's very common in classic Latin.<p>My argument is that since "senior" has been used as "someone having a high status" for thousands of years, it actually means it.
I moved from Junior designer to Art Director within a year of leaving college and getting my first job (doubled my income at the same company) I was put in charge of people who were "Senior" and had been with the company for 15 years+. It's true Senior != Expert. Personality is a big part as well Expert + Introvert != Management.