This has been rumored pretty much since Ben Affleck was cast as Batman for Batman v Superman: Dawn of Justice, but we now have confirmation that Affleck will direct a new standalone Batman film. In addition to directing and starring, he is also co-writing the script with Geoff Johns.
Johns is definitely no newcomer to the DC Universe as he's served as the chief creative officer for DC Comics and has written storylines for Green Lantern, Superman, Aquaman, The Flash, and Batman. In addition to comic stories he has also written treatments for comic to television adaptations such as Smallville, Arrow, The Flash, and the new Supergirl series.
Prior to any solo Batman action, Affleck still has to direct the Dennis Lehane adaptation, Live By Night, so it seems the 2018 date is most likely true. In addition to co-starring in Batman v Superman, he will also suit up as the Caped Crusader in the two-part Justice League film directed by Zack Snyder.
Personally, I am not the biggest Affleck fan in general but I will admit that he is a talented director. As far as him being Batman, we don't know until March how that worked out. Obviously the studio seems behind it or they wouldn't have put this much at stake with Affleck's involvement.