I really think that Hook’s child is older because Hook was an old man, then they were all in the Enchanted Forest for 10 years after Lucy was born. Hook should be about 70 years old outside of his time in Neverland. His daughter is probably older.
The only assumption we can make is that the oldest Wish Hook’s child could be is around 30. The Wish Realm veered off course when the Evil Queen was defeated and no curse ever came. So Wish Hook met and impregnated some woman and then that daughter was stolen. I’m assuming the rum belly and aging badly came from his despair over losing his daughter to the witch after she found out he was sneaking in to visit her.
I still think Anastasia is his daughter. We don’t know how long she’s been ‘dead’, but I’m assuming she was close to Drizella’s age, which would put her in her 20’s if she hadn’t ‘died’.