The County's median age rose by 2.7 years between 1990 and 2000—to 37.4 from 34.7 years. Census tracts with the highest median ages are concentrated in central-west and near southwest areas of the County. In the central corridor from Ladue to Chesterfield is a swath of census tracts with above-average median ages, in many cases at least five years above the countywide median. High median ages are also found in near southwest County, especially between Watson Road and Interstate 55 in the Affton, Crestwood and Sunset Hills areas.

Higher median ages are typical of established neighborhoods, especially where larger single-family homes predominate. Newer housing tends to attract younger families with children, while more established neighborhoods have more “empty-nester” households whose children are grown. It should be noted also that the presence of nursing homes and retirement/assisted-living facilities contributes significantly to higher median ages in some tracts.

Near North County is the exception in the aging trend. That area has the greatest number of tracts with median ages at least five years below the County median. In North County areas south of Interstate 270 and east of Lindbergh Blvd., median ages below the countywide median predominate. Lower median ages in inner-ring suburbs in the northern portion of the County suggest an influx of young families to older neighborhoods in that part of the County.