Have you ever watched Gotham and thought "Man wouldn't it be cool if [The Flash](series:1068303) just showed up?" But then you remember that they're not in the same time zone. But are they? I've read my fair shares of comic books and done the research, and that question could actually make a lot of sense.
Most likely you've watched The Flash TV show and you know that it revolves around Barry Allen. Well Barry Allen eventually dies. I know, I know, it sucks. But that's okay, because it backs up my theory really well.
Because of the death of Barry Allen he obviously couldn't join the Justice League, His nephew took his roll. Wally West, popularly known as Kid Flash, who was actually the same age as Bruce Wayne Is in [Gotham](series:1127075) when he was helping out Barry. Which gives both Wally and Bruce Time to age, and do there own thing (Like turn into a bat). Well while they're aging and going to join the Justice League. Oliver Queen is doing the same thing. Because you gotta admit, when ever you read a JLA comic book or watch something about the JLA, you can tell that Green Arrow is the older one of the group. I mean you never see Batman, or Superman with a beard, but you Always see Green Arrow with one.