I would say that KFI has a youthful sound for an AM talk station. In fact, I bet if it were on FM, its audience would be significantly younger. Yes, I know morning host Bill Handel is 72. But the other hosts aren't that old.
What's more important is the station doesn't follow the "All Conservatives Good, All Democrats Bad" playbook that most talk stations follow. I'd say it's balanced and fun to listen to.
Being only on AM clearly skews the demos. You could have the greatest programming on an AM station but it would only have old listeners because young people almost never flip the AM-FM switch.
As mentioned above, there are a few "Hot Talk" stations that are popular. Both are in Florida: WHPT 102.5 Tampa, tied for #7 in the latest ratings. And WTKS 104.1 Orlando, #12 in the latest ratings but usually around #7 or 8. (The Holiday ratings are skewed toward Christmas stations.) These FM talk stations are are quite successful. iHeart is trying to do the same in Dallas with 97.1 KEGL, although that one is off to a slow start.