How long did the World Trade Centers stand?

The official ribbon cutting ceremony of the twin towers was April 4, 1973, however, tenants were accepted into the North building in December 1970 (the same month that the topping-out ceremony was performed), and the South building in January 1972.

So in terms of building completion itself, the North tower stood for 30 years and 10 months. The South tower stood for 28 years and 9 months. In terms of the official ribbon cutting ceremony, the towers stood for 27 years, 5 months.