The age or place you purchased your items does not matter. As long as an item is eligible for protection, regardless of its age or if you purchased it used from a store or individual, you can add it to your plan and have it protected through AKKO against accidental damages and theft.
NOTE: for electronics, parts failures are only covered for devices that were purchased new and within 120 days after you enroll with AKKO (except for phones). Older items ARE still covered for accidental damage and theft as long as they are undamaged and fully functional! (see more info here)
For items you purchased used or through a 3rd party marketplace platform such as Craigslist, eBay, Facebook Marketplace, or OfferUp, request an email be sent to you by a seller stating the date you purchased an item, the amount paid, and what the item was.
This can suffice as a receipt should you be asked to provide one during a claim. However, for any claim of theft, you must also be able to provide proof of purchase (such as a record of a PayPal or Venmo payment, or a copy of your credit card or bank statement showing the date and amount paid). Read more here about how purchase receipts are not required for coverage.