Is this a first trip for the 17 y.o? If so, I wouldn't worry at all. WDW is magical for the first time at any age.
If the 17 y.o. has been multiple times, you might want to try to plan a day or two during your trip at US/IOA if you haven't been there. It's definitely geared more toward teens and has lots of thrill rides. Mine are now 16 & 14 and prefer US/IOA over WDW, but they've been to WDW multiple times since they were little. When we go to the Orlando area we spend more time at US/IOA and Busch Gardens (Tampa) and a day or two at WDW either riding their favorite rides (Tower of Terror, Rockin' Rollercoaster, Dinosaur, Space Mountain, Pirates of the Carribean, etc) or hitting any new rides that may have opened since we were there last. If you and your spouse/S.O. are going maybe you could split up and one adult and the 17 y.o. go to US/IOA for a day or two and the other stay at WDW with the 9 y.o.