“Dragon Ball Z” saw the powerful half-Saiyan children, Goten and Trunks, fight against Majin Buu. While fans expected to see them as early teens in the sequel series, “Dragon Ball Super,” they still looked like children, and one fan on Reddit has a theory as to why.
The theory is that Goten and Trunks’ aging slowed down because they used the Hyperbolic Time Chamber to undergo years worth of training in just a few days, during the Cell and Buu Sagas in “DBZ.” This chamber is a magical room located on Kami’s Lookout where time passes much slower inside than it does on the outside.
Goten and Trunks learned the Fusion Technique in this chamber, so perhaps their stagnated ages were unintended side effects of learning how to fuse two people into one. Unfortunately, there has been no official confirmation of this theory’s validity, so the official explanation is that the boys simply look young for their age.