When you pull the whenCreated attribute from AD in a claim rule, it will show the following format: YYYYMMDDHHmmss in Zulu time.
You can transform it to MM/DD/YYYY (which is in my opinion, the worst way to store or display a date) with a RegReplace operation in a second rule.
You cannot out-of-the-box do the subtract operation. You can do that in a custom attribute store. But that's a lot of work for something that can be handle by the actual relying party.
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