What's up with this many subreddits realted to age?

Earlier there were two teen subs. Then they made two twenties subs. Then came thirties and forties subreddit. Now I'm seeing subreddits like mid twenties and late twenties. I'm in early twenties so is there any early twenties subreddit I should be aware of? Man, it's really hard to keep track of all of this, these days.