Believe it or not, people do create new email accounts regularly in order to continue posting unwanted things on Imgflip. 30 day bans would be similar to deleting accounts, which we already do when users regularly violate terms of service.
The problem though is that we can't really ban accounts for a lot of the stuff that is disliked, because it's not against our terms of service. Being immature isn't a violation, so we won't delete those accounts. It's just something that everyone goes through and so with users on the site under 18, we'll definitely encounter some immaturity.
We wouldn't want to punish people using the site normally. I think there is something to the whole back-and-forth comment thing that happens on Imgflip though. Often times, two users will essentially message each other back and forth using the comment section for about 30 comments. This obviously isn't helpful to users other than themselves. One way to alleviate this would be adding private messaging, another way would be limiting the number of comments per image when it's a simple back-and-forth that no one else wants to see. Open to more ideas.