I'm somewhat unsure of why you're posting. I don't recall anyone saying specifically that CHR stations specifically target teens and "under 25" year olds.
As for CHR following trends, maybe you don't think they have to, but they do, nonetheless. Matter of fact, if you're a program manager for a monolithic broadcast entity, let's say, um, Clear Channel, for starters. You can bet the market manager is playing whatever the corporate programmer is telling him or her to play. And, sorry to say, they do follow pop trends...it's the bane of their existence.
Regarding the urban product, WNOK was heavily dayparted up until 2001(can't say for sure what they did after I left). They were emulating Star 94 out of Atlanta. For all intents and purposes, it was Hot AC during the day and more or less mainstream CHR at night. By and large, the Columbia populace has never "run" from any urban product, but then again the product has been well researched and mass appeal oriented(i.e. John Secada, Janet Jackson, Marc Anthony, etc) before it ever sees the light of day airplay-wise.
Ultimately, WNOK was pretty much all things to all people of all ages for a long time. The general rule of thumb was program during the day to the adults 18-34, superserve the 25-34s and any 25-54 that wanted to come along was welcome. At night, it was programmed to the young people so that when they turned their radios off at night in the living room, kitchen or car, it was on that same station the next morning when the adults usually were using the living room, kitchen or car....and the cycle began again.
As for CHR being for or not being for kids, I liken CHR the way it used to be to being a well balanced diet...for all people, kids and adults.