If your HSA contribution shows on your W-2 (Box 12, Code W), don't enter the amount again when you go through the HSA section in TurboTax. The program picks your contribution up from your W-2 entry, so if you enter it again, the amount gets doubled.
This is probably why you're showing an Excess Contribution of $8300. You are correct that you are allowed to contribute $8300 to your HSA at age 55.
Here's more detailed info on HSA's.
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