tl;dr
What i have in mind, soon as ancient people learn that they can trade things with their own value like barter, discovered gold and silver or other precious stones/stuffs, people start betting and learn gambling on their own way.
It's difficult to know things like this especially for a question of "when" for a timeline since its now a history, although the "where" like the origin of some form of gambling might be a little easier.
wow.. well informative. we find so many things. please Can you provide the exact source of link about this topic.. I just want to see the main source of each topic.
If you're referring the OP, you can check the OP, there's a URL as source in the end, you can check this URL
[1] too for more reading.
If you're referring to my reply, it's what i only think. Since there's no one can tell the exact what had happened before. Barter system helped ancient people know what items have such value, so this valued item can be used as bet when they're betting in a game or something.
[1]
https://www.gambling.net/history/