No, it isn't population, and lack of skill is a symptom. If there was not increasing efficiencies, a larger population would generate more work, not less. The growth of the global population is slowing, and many western countries don't have high enough birth rates to replace who they lose. Without immigration, they would be in population retraction. The lack of local population is causing issues, if there was a need for workforce like there was twenty or thirty years ago. However, workplace efficiencies are softening the blow of a retracting population, making the lack of birthrate seem less a problem than it actually is.

A large population isn't an issue for the economy, it is an issue for preserving the environment.