I'm with BowWow. Strict exercise restriction (no running, jumping, playing, keep confined inside, leash walks only outside to eliminate), get an appointment with your vet to be seen. The listlessness along with aspirin makes me concerned. Not to mention that dose. There's much better anti-inflammatories out there. We use aspirin when dealing with IMHA dogs, not when dealing with pain. And it irks me that that guy literally has a dose for a medication listed on his site. -.-
If you wait a few days and he still is painful, then going in isn't rushing into it. Plus the better medications for pain thing. I may be more of the worry wort kind myself with my dogs (I also work for a slew of vets so it makes it easy for any pet to be checked of mine) but often it's much better safe than sorry. Could even be a little of both issues, especially if you've never really had the hips checked out. At 9, no matter how good your bone structure was to start, you likely have arthritis going on. Wear and tear is always wear and tear.