I would send them a letter for debt validation just to make sure that its not another account. It certainly seems odd for them to be coming after you after all this time. Since there is no verbiage about the age of debt on the letter, I wouldn't take any chances that this gets put on your credit report.
I am not sure what they actually will send you because I have never had someone come after me for debt that wasn't actually mine but I would assume that proof would have to include account numbers and dates.
Will a reply to a validation letter include all the need to knows like DoFD, last payment, age, etc?
Yes. They will send an itemized, detail statement of the debt.
So again, respond via "certified--return receipt requested" within the 30-day period disputing the debt and asking for proof/validation that you owe the debt.