hi the problem has been resolved. Im using a Mac Sierra 10.12.6 with a Wacom Intuos pen CTL-480 on Illustrator CC. Previously the pressure option was greyed out, so I re-installed (upgrade) the Wacom Drive to the newest available, and then I went to (I think it's called) Wacom Utility and removed all users. And I restarted the computer and the greyed out problem was gone.
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