Creating a subreddit is about as easy as creating a facebook page or tumblr blog or twitter account. Type in a name, click a button, and you’re done.
Managing a reddit community is a whole separate challenge. Recruiting new subscribers is generally accomplished by commenting on other subreddits. Popular posts can also appear on the reddit frontpage or /r/all, which tends to get an influx of new subscribers. Recruiting can also come from non-reddit communities. Most of KIA’s early users came from 4chan’s /v/ and /pol/ boards, The Escapist forums, gamergate IRC channels, and followers of certain gaming twitter accounts.
Aside from recruitment, the other big challenge is rules and moderation. The better subreddits not only have large active mod teams, but also tend to use complicated moderator bots to automatically remove rule-breaking posts. Building and managing a mod team is a real challenge. Setting up bots can get quite complicated and requires a decent amount of expertise.
Moderators are also responsible for enforcing reddit’s global rules against illegal content, harrasment, doxxing, etc. Theoretically, the entire subreddit can be shut-down (see: /r/incels). But in practice, this very rarely happens. If your subreddit has a “rule” that says “no harrassment”, the admins look at it and say “good enough”, regardless of whether the mods enforce that rule. Toxic groups also tend to use reddit as a way to build a community, and then use other websites to actually organize and carry-out their toxic behavior (IRC, slack, discord, twitter, etc.). Reddit admins also don’t really care about it. It’s fine to use their site to organize harassment campaigns, as long as the harassment itself takes place on other sites. Also, even when the admins do shut down a subreddit, it tends to be quickly replaced by new subreddits, with minor rule changes in attempts to find loopholes (again: see /r/incels).
I wouldn’t be too surprised if the creator was a 13-year-old at the time. But so much of the movement was coordinated in other places, by people with more popularity and power, by adults who have no excuse.