As others have said, this is normal for cockatiels; I'm actually surprised you never noticed it before. When their feathers grow in they are covered by a sheath, and that breaks off during preening/scratching and leaves dust on and around the bird. It is really noticeable if your bird ever flaps against a window or mirror - they will leave the dust in a silhouette shape which I find really funny, but your house guests will probably be confused.
I believe cockatoo feathers produce a similar dust. It can cause heath problems for people who are sensitive to dusts and such, but generally if you keep his cage reasonably clean it shouldn't cause any problems. Giving him frequent baths or showers will help reduce the dust too. Mine loves to come in the shower with me in the mornings! I got a special perch made to use in the shower, just be careful not to get soap or shampoo on him as it will cause skin/feather issues.