“Youngsters tend to live for the moment whilst older folks are more concerned about their futures.”
“A key difference emerged between participants who were aged thirteen and younger versus those aged sixteen and older, with the older group being more future oriented. There were no age-related differences among participants aged thirteen or less, or among participants aged sixteen or more, whilst fourteen and fifteen-year-olds were mixed…”
http://bps-research-digest.blogspot.com/2009/06/our-changing-attitudes-to-time.html
The younger age group tends to favour immediate reward, while the mid-adolescent & older age groups tend to value immediate rewards less.