As of today, July 1st 2020, AAdvantage miles no longer expire for members under 21 years of age.

Once you turn 21, the usual 18 month expiry policy kicks in.

Another important detail is that anyone under 21 who had miles expire after Jan 1 2020 can have them re-instated free of charge by contacting customer service.

This is a great policy as there is no longer need to track your kids expiry dates until they approach age 21.

https://onemileatatime.com/prevent-a...from-expiring/