an aftermarket fork most likely. Standard (full) travel for the 09 Float was 140mm. If it's at 100mm there is likely a spacer or to installed to reduce the travel. If it is and OEM fork, it's not that certain, but still a good possibility. You'll have to open up the fork to be sure though.
The only way to know for sure if you can extend your fork is to tear down the fork and see if you have any spacers installed which can removed, and see if the damper can extend far enough.
Yes, you can limit travel down by installing a spacer.