Ten to Thirty Years Wear of action parts continues, the extent depending upon how hard and how often the piano is played. Normal regulation and voicing will maintain good tone and touch if usage is moderate. Years of seasonal changes cause bass strings to sound dull and treble tone to lose clarity. Eventually, adjustment alone will not correct these problems, and some parts will need replacing to restore the original tone and touch. The needs of the pianist are the real variable in judging a piano's useful life.
Good performance requires a piano in good condition.
Even economy grade instruments can often be dramatically improved by judicious reconditioning. Your piano technician can help you make this decision. Eventually, it becomes less and less practical to continue maintaining a very old piano. The undeniable end of a piano's life comes when the repair cost exceeds the value of the repaired instrument. Medium quality old uprights reach this point sooner than do high-quality large grands.