The only thing I would counter to Derek's advice is - what happens if the Expected Closed Date comes FORWARD in time? Then the FIXED calculation will return the MIN which in theory could be an Expected Close Date reported part way through the year.
If you truly want the first date for the opportunity ID, you should use a Tableau Calculation, I'd suggest the combination of LOOKUP and FIRST - Table Calculation Functions
I.e. LOOKUP(attr([Expected Close Date]), FIRST())
Your syntax is definitely wrong, I'm not sure what you're trying to do. Please take a look at the documentation on the LOOKUP function.
The lookup calculation will look SOMETHING up (that's the first parameter to the function) based on an offset (the second parameter).
You then need to setup how the table calculation works once you've added that field into your report - See more on table calculations here Understanding Table Calculations