According to the theory, 'passive savers' (those automatically enrolled in 401ks) may not develop a saving habit and often delay retirement saving until around age 35 when they earn more.
"the author argues that passive Savers are not building a habit of saving money because they were forced to save therefore most people won't choose to start saving for retirement until a later phase in life and the age of roughly 35 when they start making more and they can catch up without a change to their lifestyle"