Despite the myth that wood is the most venerable material to make windows from it is a fact that original Georgian and Victorian windows which are over 100 years old are still intact.
The oldest surviving examples of sash windows were installed in England in the 1670s, for example at Ham House. In fact is it very possible that wooden windows installed today by a credible source will last until maybe 2440!
Wood is the most traditional type of material used to make window frames. Wood frames are great for insulating against heat and cold. Moreover wood is especially suitable for unusual sizes or window shapes particularly when replacing like for like windows in conservation or listed buildings. The detail that can be wrought from wood such as sash horns, glazing bars and checkrails would not be possible to replicate in other composite materials such as PVC or aluminium.
When properly treated at manufacturing stage for moisture content and preventative fungal and insecticide damage and correct paint the expected life of the window without maintenance is 4-6 years. Ref: http://inspectapedia.com/BestPractices/Table1-15.jpg