Aluminum does not rust. It turns to aluminum oxide which is white in color and will separate easily from the aluminum, often as a dust. It also doesn't go deep like rust in iron does. It forms a barrier so once a bit oxidizes, that's it. Don't clean it off or it will just happen again and you'll lose a little bit more structure each time (though so little each time that it would take a long time to be a problem, but why bother with it?)
I live in MA and notable rust on a 5 year old car is NOT right even if driven in the winter.
I can almost guarantee you that the problem is that it was left parked on dirt for periods of time. NEVER, EVER do this. It WILL completely rust out a car in a year or two. I did it with an old winter beater of mine because I had no place in the driveway to put it. The engine got tons of rust, the brake and fuel lines rusted through, and the frame was pretty bad (though intact). The car could have been fixed but it was worth very little so I didn't bother.