^ Nothing difinitive, but his statement of:
“I would say in terms of making any character decisions on ‘Apocalypse’ is, we set back the clock on ‘Days of Future Past,’ so a lot could have changed from that point in 1973 forward, meaning people could have been born earlier,” Kinberg said. “The whole world changed after those events. Things that were represented even ‘X1′ and ‘X2′ and ‘X3′ wouldn’t have happened in quite the same way.”
Seems to indicate that some character, that might apply to Apocalypse, who we didn't see in DOFP after Wolvie woke up (we did see Cyclops, Jean, Storm, Kitty, Colossus, Rogue, Bobby, and Wolvie), nor wasn't from the 1973 timeline (like Mystique, Beast, Havok, Toad, etc.), and further, that we've seen previously in X1 through X3, will be born earlier in order to make him/her usable in 1983.
If it was solely being "not bound by the continuity of the past films" and nothing else, then his quote would not have very specifically included "people could have been born earlier". That statement holds meaning!
Now all you need to do is list which characters we've seen in X1 through X3 that weren't in DOFP nor in the scene after Wolvie woke up, and then determine which of those characters apply to Apocalypse.
I've got a feeling you might come up with say, one specific character that meets these requirements...