I sell cabinets and wood components for a living. Yes it looks to be me like the natural wood areas on the playfield have aged. Areas that don't receive sunlight will stay about the same color as when the playfield was first made. Lighter colors stains or natural wood tend to show the most drastic change. Yes, you can age the unexposed wood by laying it out in the sun for short periods at a time - we do it all the time for cabinet doors especially cherry. I would recommend covering the rest of the playfield or it could darken even more than it already has.