There is no maximum for paper.
There is also no maximum for Bitcoin because you can continue to divide it into smaller increments. Similar to how a stock can split. So while you could say it's 21 million (minus the amount that is lost permanently), this doesn't tell the whole story because you can always add another decimal place.
Dividing a unit infinitely (Which is not the case with Bitcoin anyway) doesn't make it unlimited, since it's still the same 1 Bitcoin.
