I would agree with what most have said. The biggest problem with most scooters is neglect. A scooter that is run at least semi-regularly will likely last a very long time, as it seems many of the biggest problems arise when the machine just sits for too long.
Along those same lines, the manner of storage plays a big role. I would think a well-maintained scooter that is driven regularly and garage kept out of the elements, could easily run for a decade if not two with no more than regular maintenance and replacement of normal wear parts such as tires, brakes, filters, cables, grips, etc.