Byblos was a city in Phoenicia (now Ǧubayl, Lebanon) that has been inhabited since about 5000BC — perhaps is the oldest continuously-inhabited city in the world. Byblos was a centre of publishing for a very very long time: the name Byblos in fact comes from the Greek word for papyrus.
In around 1800BC, a script was used in Byblos with 90 to 120 glyphs — about the right number for a syllabary. There are few enough examples of the script that it has not been conclusively deciphered. (A few people think that they have succeeded, but the deciphered text sounds so clunky that many experts are unconvinced.)
One thing that is distinctive about this writing system is that Byblos script had short vertical bars between words. As far as I can tell, this was the first writing system which marked word boundaries. Other writings systems had determinatives (which could act to demarcate some of the words), but I have not seen interword separators in older scripts. (NB: most people don’t find those interesting or important, so it just might not have been mentioned.)
It is possible that the Phaistos Disk uses boxes to separate its words, but the Phaistos disk script is even more poorly understood than Byblos script, and its age is unclear.
In the modern, Latin-script world, we take interword separation for granted, but it is not at all obvious that words need separation. Normal speech is a succession of continuous sounds; there is no pause between words. It takes some effort to teach Latin-script-using children to insert spaces into their writing. Many languages in use today do not use any form of interword separation, including Chinese, Japanese, and some of the Indic languages.