No, it isn't dangerous to vape expired e-juice, nor is it bad for your health. It is simply a recommendation by the producer. This answer settles a major myth in the vaping community on if vaping expired vape juice is dangerous for your health.
Both VG and PG have a shelf life that --at maximum-- lasts about two years at room temperature. This means that vape is reasonably durable, but it's no can of peaches. It will eventually go off, opened or unopened. But long before vape officially expires, the flavor can become stale.