User blog comment:RocksisDragonOP/Rocks D. Xebec IS MONKEY D. DRAGON/@comment-115.240.192.150-20200424113140/@comment-189.27.133.236-20200425225016

Dragon's age and being still alive could be an effect of Booney's Devil Fruit. Perhaps she decreased his age to that of a babe/child and Garp adopted him instead of killing him.