Date of first delinquency means the date when you first had a late payment on the account. Credit reporting agencies may not report anything older than seven years, so late payments made since then are noted with DFD.
Date of last activity is any use of an account in the last seven years, whether it is an on-time payment or a late payment. Accounts with no activity are supposed to drop off your credit report after seven years. Simply calling a creditor does not count as activity.
Negative Activity on Your Credit Report
The Fair and Accurate Credit Reporting Act of 2003 states that creditors must wait 180 days from first delinquency before posting negative activity to your credit report. This is to provide a grace period to consumers.