Originally Posted by
Badou
Because she is the iconic Batgirl and DC wants to market her as being Batgirl. So they want to keep her in her early 20s so they can keep her college age where the Batgirl title still feels appropriate, and that is how she is being written. She isn't going to be written like she is in her early 30s like she was pre Flashpoint.
Dick is the same age as her, but he also isn't Robin anymore and is Nightwing. So they are sort of forced to write him as acting a little older as he has Jason, Tim, Damian and even Duke now all after him as being Robin or some version of a Robin in the Batman books as being younger than him.