While we really should just ask the original author to explain, my interpretation is: younger employees are more likely to simply acquiesce to unreasonable demands like short notice for working late. Or working to prove themselves bc they lack confidence.

Older workers have gained the confidence to ask for what they are worth. Employers do not appreciate this. They may have a more efficient way of working or may not have a singular definition of self (work == my identity) and obligations like family outside of work.