What is the lifespan of a skylight?

Depending on material and location, Solar tubes and skylights can last around 10-20 years. Skylights and solar tubes should be updated at least as often as the roof. An old leaking system can damage the integrity of a new roof very quickly leading to replacement and repair on both unit and roof as well as an interior damage.
 
As with all household things, regular maintenance is important in keeping skylights and solar tubes in working order. You should have routine inspections of skylights and solar tubes to make sure they are in proper shape (only inspect them yourself if you feel comfortable doing so).  Make sure solar tube and skylight flanges/curbs are holding up.  Look for any lifting or separating. Check for and remove leaves and debris from the surrounding area. If your skylight opens, make sure that the seals are clear of debris and are not cracked or torn. Check solar tube collectors for cracks and separation. And of course, check indoors for obvious leaks, bubbling, or discoloration of surrounding areas.