Yes, normally you can still purchase GAP insurance for a motor vehicle even though it has been 5 months since you have purchased it. You can purchase GAP insurance at anytime as long as the GAP policy requirements are met.

GAP insurance can provide valuable protection during the early years of your car's life. If a covered loss occurs (theft, total loss in a collision, etc.), GAP insurance will pay the difference between the actual cash value (ACV) of the vehicle and the current outstanding balance on your loan or lease.