We here see a world where people stop physically aging when they reach 25 and have a year to live unless they get more (or less) time. Money is replaced by time as currency, and the reason the setup is such is left unexplained, though the hint given is population control. It also appears as if the situation can't be changed.
This beautiful concept is fucked by a lazy plot and stupid casting choices (the people were supposed to look 25). The best fun in the movie can only be seen in the early scenes, but then the overly-courageous acts and extra skills of the Justin Timberlake character were left unexplained... lazy writing. Luckily it's not boring, even to the end.