As of June 25th 2017:
ALL old licenses and SketchUp Maintenances EXPIRED past 3 years will no longer be eligible for upgrade or Maintenance renewal. This policy will be ongoing, and will apply to all Maintenances that are left to expire past 3 years. The license itself will not expire, it wil continue to work as it always has, but you will not be able to upgrade it or install it on any new devices. In order to obtain the latest version of Sketchup Pro you will need to purchase a new license.