"this game has been in development for almost 10 years"
That would imply it was started in sometime in 1995.
"DNF was announced before the kids, who are in High-School now, were born."
That would imply it was announced approximately 15 years ago, or 1990. 3DRealms didn't even exist in name until 1994. The original Duke Nukem came out in 1991. I don't see how a sequel could've been announced for a game that was still a year from release at the time you say it happened.
The earliest I can find a reference to Duke Nukem Forever is 1997 when it was announced as a new side-scroller. When that was axed 3DR repurposed the name for the current Duke non-entity. That's seven years after you say it was originally announced.
1990 was the freakin' dark-ages for PC gaming. Diamond wouldn't release the Monster3D for close to six years, games came on 3.5" floppies, ran under DOS, and were still using VGA graphics. I think the very first Commander Keen was released that year (or late '89..hard to remember). The fact of the matter is, though, that you are exagerating things pretty badly.