User blog comment:RocksisDragonOP/Rocks D. Xebec IS MONKEY D. DRAGON/@comment-35870268-20200424005951/@comment-189.27.133.236-20200425225030

I had thought about that too. His age being too low could be an effect of Booney's Devil Fruit. Perhaps she decreased his age to that of a bay/child ans Garp adopted him instead of killing him.