Listeners age 25 to 54 continue to thrive as the “sweet spot” for radio, while consumers in cell phone only (CPO) households continue to listen at a higher rate than the 12+ population, according to an analysis of the spring 2010 ratings in 51 markets released today by Nielsen.

According to data released today by Nielsen’s new radio ratings service, which measures radio listening habits in 51 small and mid-level markets, 18-34 year olds in these markets listen to the radio 21.5 hours each week.