In the novel, the age change of Baochai and Daichai was that when Baochai and Daiyu first met, Baochai, Daiyu, Baoqin, Tanchun and Miaoyu were all thirteen years old, and Baoyu was twelve years old. In the Red Chamber, the age difference between Baochai and Daiyu was three years, specifically, Baochai was fifteen years old and Daiyu was twelve years old. As for the date of his birth, the text did not give any specific information, so he could not provide it for the time being. However, if you want to know more about the novel recommendations related to Dream of the Red Chamber, you can tell me ~ I will try my best to recommend suitable works for you. I hope you like my recommendation. Muah ~