Dwarf Giants have not come directly from the pairing of a Dwarf and a Giant in centuries, so far as anyone knows. Most originate from the Dwarves in Jotunheim before and shortly after the Wall of Winds was conjured at the end of The Iron War, mostly in the south of Jotunheim.
They are vanishingly rare south of the Wall except for the northeast of Nidavellir in the Amar Mountains. Giants and Dwarves mature at significantly different rates in their societies, but physically at similar rates, and would be considered adults by the standard of who raised them. They share their Dwarven ancestor's love of craft, mountains and stone, and their Giant ancestors love of solitude and cold, windy places.
Growth Rate & Stages
Character Building: Dungeons & Dragons 5E
How to build your D&D 5E character in the Realm of Beardsgaard