I don't think your parameter has been created from any date field. If it would have been created from any date field then max date shouldn't exceed from Today's date.
Lets take an example of Superstore data. If you create a date parameter on [Order Date] then you can realise. Max date wont exceed the today's date. Here data is till 2014. You can try this with your date field.
If you create a date parameter without using any date field then you can specify you min and max date as per your wish. Or by default tableau specify your min (today's date) and max (date after 100 days from today's date)
If you calculate date diff then you'll 100 days between #04-11-2016# and #12-02-2017#
Hope you get my point. Let me know If you've any query.
Mahfooj, Date fields can and commonly do have dates greater than today.
I don't know what I'm missing here. My data sources date fields have dates greater than today. For example if we are looking at expiration dates, that would be a date field that will have dates in the future, but there are countless other reasons why date fields have dates in the future.