Aluminum and vinyl sidings - will not peel and will not need painting for a long time, but both types of siding will definitely oxidize (or "chalk") due to sunlight and weather breaking down their pigments. Eventually, oxidation will destroy the factory-applied paint.
These kinds of sidings also discolor when they collect coatings of soot, industrial sulfur, pollen, rust, and especially mildew, either in shadowed areas or where water runs down.
However, siding's color and luster can last indefinitely if it's kept clean and waxed. The Institute of Vinyl recommends yearly cleaning in order to keep warrantees valid on vinyl siding.
Unfortunately, delaying the cleaning of siding has consequences. The longer the job has been put off, the more difficult it is to remove soil. Multiple scrubs may be required.
When we clean aluminum and vinyl siding, we scrub with specially formulated biodegradable cleaning solutions that are meant for vinyl and aluminum. We use airless sprayers to apply it, reducing overspray and runoff.
We wash from the bottom of the building up. It's a little counter-intuitive to many people, who think it's a good idea to clean the top first so the dirty runoff doesn't re-soil any clean lower surfaces. But it's important to remember that the runoff also contains cleaners, which can leave streaks wherever they drip over dirty surfaces. On some surfaces (including brick) and some colors of siding, particularly reds and browns, the streaks can be tough to eliminate later. So we've learned how to do it right: bottoms up!
Painting aluminum and vinyl siding? It can be done, but we recommend it only if you really want a color change. Remember, you'll have to repaint those surfaces regularly once you cover the factory surface.
So, when prepping aluminum and vinyl for painting, we add an additional step to the cleaning process --- acid etching of the surface for maximum adhesion. And we use specially formulated latex paints that are meant for those kinds of materials. The special paints are needed because aluminum and vinyl siding expand and contract more than wood does, and the paint needs to be particularly flexible.
