Can't confirm purchase date

You will only find that in the invoice that you received when you bought the device. If you have lost it...

Log into Apple

1. Click on the bag icon as shown in the above
2. Click on Sign in
3. Click on Orders
4. Click on the items that you want an invoice for.
5. Click on View Invoice under the Order Number Top right-hand corner. See the pic below...

There you have it.