A Reuters-Ipsos poll from 2014 found over 1-in-3 people under the age of 30 lending support to the idea of their state seceding from the union, compared to fewer than 1-in-6 people over the age of 60 feeling the same way.
A recent SurveryUSA poll out of California corroborates this. The percentages of Californians, by age cohort, who are opposed* to Calexit:
Hispanics, with 25% supporting, are the most likely to favor Calexit. Whites (13%) are the least likely to do, with blacks (16%) and Asians (18%) falling in between. Men (21%) are more likely than women (15%) to favor it.
* There are three responses to the question, "remain", "withdraw", or "not sure". This table lists only the "remain" percentages and thus may appear to overstate support for secession. The full results are here.