I have been told that a lease in the Shariah is not permissible for more than three years.

Answer

A lease may be for any duration of time for private property. For Waqf property or the property of an orphan, the maximum duration is three years for land, and one year for property (house, shop, etc.). However, in today's time the benefit of the Waqf shall be taken into consideration. If it is beneficial to have a long lease of three or five years for a Waqf property, then in our opinion it will be permissible. But longer than five years will not be permissible for a Waqf. And Allah knows best.