Board Thread:Episodic and Issue Discussion/@comment-47881-20131118225102/@comment-1038387-20160325173248

We don't know the exact timeline. We know Dick was still Robin in October 2012, and Tim became Robin in early 2015. At that point, Jason was already dead. Legacy takes place in February 2015, shortly after Tim became Robin.

That's where we get vague. We can assume Jason didn't come along until after Dick became Nightwing (I think). At what point did he become Nightwing? Not on his 18th birthday. That was December 2014. Maybe his 16th? That would allow for a two year gap for Jason.