The graph below shows the number of people in Washington State who voted, graphed by year of birth. As you can see, most of the voters are about age 60. There are not many voters of age 18 through 38.
Overall, 3,396,040 Washingtonians voted from 2012 through 2014. Of these voters, 1,932,662 of them were born during the twenty year period ending in 1966 (these people were between 48 and 68 years old in 2014). Only 872,286 of the voters were born between 1976 and 1996 (people between the ages of 18 and 38). Only 460,986 of the voters were between 18 and 30. For every 1000 voters between 48 and 68, there were 635 voters between age 18 and 38.
Restricted to King County, 392,001 voters were between 48 and 68; 303,176 voters were between 18 and 38. For every 1000 King County voters between 48 and 68, there were 773 voters between 18 and 38. So, the turnout in King County for younger people is somewhat better.
It’s true that there were many people born in the 1950s (the baby boomers). Does this account for the high ration in the number of elderly voters compared to younger voters? Apparently not. The chart below (from the U.S. Census’ bureau’s article Age and Sex Composition: 2010) shows the population of the United States by age group for the 2010 census. As you can see, for both males and females, there were peaks in the number of people at age 50 (the baby boomers) and at age 20 (the children of the baby boomers). There are more women of age about 50 than of age about 20; there are slightly more men of age about 20 than men of age 50. But the population of men and women drop off rapidly after age 50 or so.
Note: to calculate the voter numbers, I downloaded the Washington State voter registration database (about 500 MB in size) from the Washington State Secretary of State; then I loaded the data into a database and ran SQL queries. See https://www.sos.wa.gov/elections/vrdb/VRDBFaq.aspx for an FAQ about the database.