Interestingly, the change of opinion is seen within all age groups: those in the age group of 18-29 years saw the percentage in favour increase from 45% in 2003 to 62% in 2011 while the percentages in the age group 50-64 rose from 27% to 41%.
The recent PEW-data give a highly detailed insight in the US-opinions on same sex couples. We learn for instance that Catholics are on average much more tolerant of gay marriages than Protestants, but the most important divide is the political divide with 26% of Republicans favouring gay marriage opposed to 57% of Democrats.
For Obama's campaign coffers it is noteworthy that generally those Americans with higher incomes are more supportive of gay marriage: in the income group of $100.000+, 58% are in favour against 35% opposing. Under $50.000 the distribution is roughly 50/50.