What cognitive biases reduce savings?
A study of  Gopi Shah Goda, Matthew Levy, Colleen Flaherty Manchester, Aaron Sojourner, and Joshua Tasoff (2015) The Role of Time Preferences and Exponential-Growth Bias in Retirement Savings showed that in the US the most important cognitive bias is the exponential growth bias.
Exponential growth bias is bias that occurs because people intuitively do not understand exponential growth. So when people save they think about growth intuitively in linear way.
I don't know if there is a study that says it affects younger people more, but I think it would make sense since more time difference between present and future also means a larger difference between exponential and linear growth.