As they age, diethyl ethers and other ethers form dangerous organic peroxides, so it is usually advise to get rid of them after six months. The peroxides are shock sensitive explosives and have been known to detonate even by just twisting the bottle cap. In combination with ethers, which are themselves quite flammable, it is not a great combination.
After 3 months, the risk is probably not great of some catastrophic event as long as you have stored it properly. But, if you no longer have use for this chemical, I would still dispose of it. You may test for peroxide content with an iodine assay. If this is a home use chemical, you may contact your local hazardous waste disposal organization.