And how do we know you're old enough to have the parental lock off?

I think you might draw a blank on this one here.

As you know, Duke is a pretty violent, bloody, sexual game, leading 3dRealms to include an option to turn off the adult mode, thus eliminating all the blood, gore, and nudity. When the parental lock is first turned on it asks you to enter a password so that you can turn it back on again, thus there is no one password that will turn it back on for everyone. If you forget this password the only way to turn the Parental Lock off is to reinstall the game ~ directly from the Internet. (In some versions of Duke sold in Australia you cannot turn turn the Parental Lock off. If you have this version, you need to download the USA / UK version).
You can download DN 3D as a zipped file here http://www.robbernard.com/duke/shareware.html