@Bored-chan he is probably in early 20 or just between 20-30. We need to remember that the author is Asian and they really can look young for a long time so I wouldn't be surprised even if he would be 30+ 😅 also he probably found her power to became a dragon thanks to that ring so he wants to keep her in family so no one else will use her against them and being his daughter is safe position in the family.  Also he is a psycho and thinks she is funny and interesting so he wants to keep her close for his own entertainment.  
It's all my thoughts,  I have no idea if it's real 😅🤣

@Ms.Potato it's on "chrysanthemum garden". I can't put link here so just write it in Google and you will find it right away 🤗