(Washington, DC) This graph shows two trends: the number of US citizens between the ages of 18 and 29, and the number of 18-29s who voted.
The number of young voters fell from 122 million 1972 to 114 million in 2012, despite an increase of about four million in the number of eligible citizens under 30. That means that young voters had considerably less clout in 2012 than in 1972. They cast 24% of all votes in 1972 but 19% in 2012.
On the other hand, the comparison would look better if one set 1976 against 2008, because the latter was a stronger year for youth turnout. In 2008, the size of the youth population also surpassed the previous highs of the 1970s, producing record numbers of youth and of young voters. But the youth share was still smaller in 2008 (at 16%) then in had been in the 1970s, because of rapid growth in older generations. And then 2012 saw a fall in turnout.