Classical retention time in Outlook for deleted emails is 14 days.
I would like to know how old the earliest emails are that can be retrieved using pst corruption tools (or other).
Who told you that the retention time is 14 days? It will remain in Deleted Items folder until you delete from there.
after you delete the mails it will remain only for 30 days and will be deleted automatically
set by admin
the retention time is set by admin, so it can be 15, 30 or whatever.
Admin sets the Retention policy
The retention policy can be set by admin, By default it is 14 days and with the help of pst recovery tools you can recover emails even after retention period expired. Different PST Repair Tools uses different algorithms so it is not quite sure how old emails can be recovered with these tools. I have used Kernel for Outlook PST Repair tool in the past with success with emails deleted 1 month back.
Updated - 12th Dec