There was a thread about this a couple weeks ago I think. It seems to be pretty common. Although age and feeding schedule probably plays a role, I think environmental triggers may cue the snakes to shed also. 4 of my snake's shedding were within 2-3 days of each other from September until springtime. Sometimes in September last year, there was a very chilly day, and about 1 week later all the snakes shed in unison and stayed together (Emily is older and she would shed ever other cycle, very strange). The snakes never had any contact with one another but they were all in the same room which had a nice big window (maybe daylight hours have an effect?).
I could be reading too far into it, maybe it's just coincidence. Now that it's Spring, Chai and Emily (both 300g+) are shedding together and Lilly and Alex (50-100g) are shedding together! I definitely have to start recording their sheds again, when I moved in April I lost my binder and didn't start again.
It would be really cool to see if anyone with a larger collection has seen correlations in their snakes shedding, or due to temperature, breeding seasons, etc.!