In the county, the population was spread out with 22.7% under the age of 18, 9.0% from 18 to 24, 28.9% from 25 to 44, 26.7% from 45 to 64, and 12.7% who were 65 years of age or older.  The median age was 37.8 years. For every 100 females, there were 115.9 males.  For every 100 females age 18 and over, there were 127.5 males.. Which age group was the least to populate the county?