If you’re an American AAdvantage member and you’re Under 21, your miles don’t expire. If you’re a United, Southwest, Delta, Hawaiian or JetBlue member your miles don’t expire.
But if you’re a lifetime elite member of American AAdvantage, having accumulated over 2 million miles, you have to stay on the treadmill of either earning or burning points every 18 months to avoid losing all your accumulated points.