That is if we count the development of D1 which appeared in 1999. Later in 2007 D2 emerged with breaking changes. D1 was discontinued in 2011 and D2 became simply D. So, yes formally D is 20 years old but one could say that it's newer reworked version is just 12.
I started on D 20 years ago. It was a couple years before I even managed to make a prototype that people could play with. 20 years ago it was a few notes on a piece of paper :-)
