You can go
here find out the SOL for your state. Figure out which accts are out of SOL and start with those. You determine if the acct is out of SOL by the DOFD (date of first delinquency).
Please be aware that disputing any accts that are still within SOL could possibly wake up a sleeping giant and you can be sued. So proceed with caution and make sure you understand what you are doing first.