From Longman Dictionary of Contemporary Englishsomething of five/many etc years’ standingsomething of five/many etc years’ standingLAST FOR A PERIOD OF TIMEused to show the time during which something such as an agreement has existed an arrangement of several years’ standing → standing
Examples from the Corpus
something of five/many etc years’ standing• The medical superintendent of a hospital had to be a duly qualified medical practitioner of five years' standing. 