There are limits even to "comic book timeline". Damian shouldn't even exist, as far as I'm concerned, and Grant's pushing things way past breaking point in saying that Talia's been able to hide Damian all this time (and has never thought about him or mentioned him in any of her appearances over the years, nevermind how out of character he has her acting by raising Damain to be a spoiled supersoldier monster). Damian would have been conceived around the time that Dick became Nightwing. That makes sense given when the book was published (Dick had already become Nightwing) and that's still what makes sense if you go back and play around with it, working with the knowledge that Batman didn't meet Ra's until Dick was in college. There's no way Damian can be older than the "Nightwing" identity. That dog won't hunt.