Many so called roof experts say 50 years or more. This comes from the Roof Tile Institute, "Clay and concrete tile roofs are one of the most cost-effective choices due to their long lifespan—50 to 100 years or more. Both concrete and clay tile outlast other roofing materials, with manufacturers offering warranties from 50 years to the life of the structure". This is so misleading and incorrect! What they are referring to is the material of the tile whether concrete or tile will last that long. Roof tiles are mainly decorative and water runs through and under them. The waterproofing and life of a tile roof is the underlayment! The life of the typical hot mopped 90lb. paper is 15 to 20 years before it deteriorates. Roofs installed with 90lb. paper will usually experience leaks from the paper failure after 15 years. A tile roof may experience leaks from penetrations, valleys and flashings which can be repaired but when the leaks are coming from the tile underlayment it's time for a new roof. This photo is from a 16 year old roof, it needs to be replaced as soon as possible even though the tiles will last another 50 years. Newer underlayments are available which come with 25 - 30 year warranties on the membrane. Roofs using these underlayments will last substantially more before the underlayment fails!