It might not hurt to open an addional AMEX card or two since they would be backdated and wouldn't ding your AAoA.   FICO scoring usually likes at least 3 open revolving accounts, with only one reporting a small balance, usually less than 9%.  

Look closely at your credit reports to see if your student loans are reporting as installment loans, usually this is the case.   You really should just focus on paying down the accounts that are reporting as revolving.