If you ask a collection agency for zero balance for a full payment on a 5 year old account and they decline will this start the 7 year clock over?

Nothing can legally change or start over the 7 year reporting time period. That time period is set by the Fair Credit Reporting Act. Certain actions can re-set the statute of limitations (SOL) which is the time period established by state law that determines how long a consumer may be sued to recover a debt.