Information from the wikis on how far in the future Batman Beyond is supposed to be, as compared to DCAU's set-in-the-'present' Batman properties, goes:
Though it is not directly stated, Bruce Wayne's final fight takes place thirty years after Batman: The Animated Series, twenty years after The New Batman Adventures, and ten years after Justice League. 
The pilot episode, titled "Rebirth," initially begins in the year 2019, 20 years after The New Batman Adventures. ... The story fast-forwards to 2039 in Neo-Gotham, a futuristic megalopolis featuring staggering high rises and flying vehicles. 
What is the source of this information?