I used the yearly reports of high school seniors' attitudes collected in the Monitoring the Future Survey, an ongoing survey of American students' attitudes and behaviors conducted since 1976. The limitation of this data-set is that it doesn't include youth who dropped out of school before twelfth grade, which varies over time.
About 90% of Boomer (seniors 1976 - 1982) and Generation X (seniors 1983 - 1999) members reported they will probably vote in a public election, when asked while they were high school seniors. Thus, the 88% of millennials (seniors 2000+) predicting they will someday vote is slightly down from previous generations of American youth.
To put this into perspective, 83% of millennial high school seniors reported they think they will eventually choose to get married. By contrast, 78% of Boomers predicted they would eventually choose to get married, while 80% of Generation X reported they expected to marry. In context of actual marriage behavior, even as attitudes about expecting to marry are increasing, a small but increasing number of people will never get married. These disparities highlight a cautionary tale that expectations of future actions do not necessarily predict actual behaviors. Notably, voting expectations remain higher than predictions of future marriage across the three generations.
The differences in attitudes between Black and White youth are narrowing. Young Black men and women are increasingly likely to predict they will get married in 2014 (71%) than they were in 1976 (57%). Black youth's expectations about voting in a public election remain largely unchanged.
White youth are also increasingly likely to predict they will eventually marry but they are less likely to expect to vote in a public election in 2014 compared to 1976. By 2014, White youth were about as likely to think they will eventually marry as they were to expect themselves to vote in a public election.