A "--" in the district column means, that the town is a district-free town, i.e. it is by itself a district.
... 30.3% under the age of 18, 8.1% from 18 to 24, 29.9% from 25 to 44, 23.8% from 45 to 64, and 7.9% who are 65 years of age or older. The median age is 35 years. For every ...