Possibly both.

After the Albany Times Union attributed NOM's 57% of New Yorkers rejecting SSM to an unusual number of old people, we decided to check NOM's poll and the Siena poll against the 2010 vote.

Here are the percentages of voters in 2010 by age (source: civicyouth.org - page 10):
18-24 5%
25-29 6%
30-44 22%
45-59 33%
60+ 33%

NOM’s poll used different ages as did the Siena poll. Still, here’s a rough comparison:

2010 Voters                   NOM Poll                    Siena Poll
18-24 5%                          18-39 7%                    18-34 22%
25-29 6%
30-44 22%                       40-49 15%                  35-54 37%
45-59 33%                       50-59 31%
60+ 33%                          60+ 38%                      55+ 37%

Our read is that NOM’s poll is probably lower than the percentage of 2010 voters and the Siena poll is probably high for young voters (based on a very rough approximation that the 2010 voter data would be 23% for 18-39 and 18% for 18-34). NOM’s poll is a little high for 60+ but Siena’s is quite low for that group (based on our approximation of 55+ 2010 voters as 44%). NOM is pretty close on the 40-49 category (We’re guessing it’s 18% of 2010 voters and NOM surveyed 15% in this age group). Siena’s number is probably about right for 35-54.

In other words, NOM's poll may skew slightly old, but Siena's poll overesamples young people, compared to actual voters in New York elections. No poll has ever shown that gay marriage is a high priority for any sizable number of New Yorkers. Or that New Yorkers prefer to leave this issue to the legislature.