As long as there is a "Catch-All" sub-forum, splitting the ages further would never work, as most sellers would slowly gravitate to the All-Ages to ensure one thread per sale.
My thought is that since this change was made to alleviate the increase in sales threads, and the "front page bump" that was killing the forums, then splitting it in two should more than do the job.
No matter what comic-based item it is, was it produced before or after 1980? Comics, magazines, Overstreets, toys, art, etc. is it before or after 1980 - done! And yes, a few sellers will have to create 2 threads, but tough tittie said the kitty, we're all out of milk!