This is all from what I understand, and to the best of my knowledge. None of it is intended to be legal advice.
The 7 years starts from the last time a payment was made, or the last time you acknowledged the debt. For example, if you last paid in 03/2005, but your cell phone provider called you and you acknowledged the debt on 07/2005, then the 7 years starts there. That's why they record the phone calls.
If you've gone 5 years, and you don't need to apply for credit, I wouldn't even worry about it.
Also, never pay a collection agency. They buy debt for pennies on the dollars. The original creditors have long written the debt off.
Most collection agencies, purchase your delinquent debt for pennies on the dollar. You don't have any agreement/contract with the debt collector or collection agency. Your only agreement/contract was with the original creditor.
If a collection agency shows on your credit report, then the Fair Credit Reporting Act says that Credit Bureaus have to have written documentation verifying the debt. If they don't, they have to remove the debt from your credit report.
If you dispute a debt and ask for verification, these have to go in your file. The Credit Bureau will likely say they don't have to have documentation, only verification. That isn't true. Keep at them to send you written documentation showing verification to remove the debt from your credit report, or you'll take legal action.