The only Advantage might be that  you get a bonus 

American’s frequent flyer miles earned before July 1, 1989, were never supposed to expire. They’ve even set aside the old award chart—frozen in time—for folks with miles that are more than 23 years old. That all comes to an end November 1, when old miles will be converted  to current miles, with a 25 percent bonus. If you have any old miles and want to claim spectacular awards, such as 120,000 miles for two round-trip business class tickets to Europe or 175,000 miles for two round-trip first class tickets on Qantas, you have three months left to issue those tickets.