Answer:
299,398,484 total population
225,746,457 total population over 18 years
122,394,724 total number of US citizens that voted in 2008 election
= 54% of population voted.
Between 22 and 24 million Americans ages 18-29 voted, resulting in an estimated youth voter turnout of between 49.3 and 54.5 percent.
Sixty-six percent of young voters cast their ballot for Barack Obama, the largest-ever showing for a presidential candidate in this age group.