That page is kind of obsolete. I think Jim Lee was speaking in general, not literal, terms.
In the old DC ratings,
Teen meant 12+
Teen Plus meant 15+
And DC covers all used to be marked Teen or Teen Plus.
They announced a change maybe 1.5 years ago, but it took time to filter down to things like comic covers. The covers were still saying Teen and Teen Plus even a few months ago, but not anymore.
The current system has been described on the first page of DC Previews (now called DC Connect) for a long time. That system is:
DC Graphic Novels for Kids - Intended for readers ages 8-12
DC Graphic Novels for Young Adults - Intended for Readers ages 13+
DC - Intended for readers ages 13+
Black Label - Intended for readers ages 17+
("DC" refers to the monthly printed comics.)
And finally, DC comics do now all say 13+ on the covers.
You can see the ratings in the current DC Connect #3 located at:
https://www.dccomics.com/sites/defau...Oct_comics.pdf
By the way, before the line renames, DC Zoom was rated 8-12, while DC Ink was rated 13-18. So the only change is the Young Adults are now rated 13+.
I never noticed whether individual comic issues were labelled Teen vs. Teen Plus, or if it was just applied as a blanket to a particular title. Presumably writers were given guidelines of some kind, or the books were rated afterwards by the editors or other in-house experts.
So in theory by setting all comics at 13+, the formerly Teen (12+) comics are more mature, while the formerly Teen Plus comics (15+) have been made less mature? I haven't actually noticed any change.
The justification for the change in definitions was to align their age ratings with the MPAA ratings system.
In practice there probably isn't a real change. Unless they do very non-obvious things like apply some different limits to the number of panels with blood or other kinds of violence, and have altered the allowed counts slightly. (That's the sort of thing the MPAA does, though I think the exact criteria they use remains a secret.)
It is interesting that DC and DC Graphic Novels for Young Adults have the same 13+ rating. The YA books actually often deal with more mature, or at least more charged, themes, applicable to young adults. And many of them have explicit language that you will never see in a "DC" labelled comic (where such words are replaced with the usual $%^&$# kind of stuff).
Some books still don't quite fit, like Superman Smashes the Klan, which originally appeared in 3 little books rather than one YA book, rated E for Everyone. DC still does put out some E books from time to time. So, while they definitely DO have this current system, there are still exceptions - which I'd guess are mostly books written before this system was established. I think their intention was to eventually transition everything to this rating scheme.
But now, who knows. DC barely gets one set of standards in place before it is already switching to another.
BTW if you've ever wondered if it was your imagination that at least some Marvel was written for a younger audience, consider that their T rating means:
T – Appropriate for most readers, but parents are advised that they might want to read before or with younger children.
Spider-Gwen / Ghost-Spider is rated T, so if you ever read that title and wondered why it seemed kind of .... young, now you know why!