It’s going to sound so wrong, but back when Snow White was first written, it was during the time when child marriage was acceptable and there is no middle stage known as teenagerhood (it’s a very recent concept in human history). As soon as you could work, you would be considered an adult even if you are 12. If anyone has read the book or seen the movie The Master and Commander (which is set during the Napoleonic Wars, same time as when Snow White was published), there are naval cadets who are like 12 and 15 years old, and the much older ablehands refer to them as “sir”. That is a historically accurate depiction.

I’m not making excuse by the way, but it explains a lot as to why older stories have very weird portrayal of underage characters because it reflected the social norms at the time. Many fairy tales in their original forms are very brutal and no-holds barred because people back then grow up way too fast as expected by society. And the gruesome reality of living, without the modernity we take for granted today, had to be faced by most folks in the past. Child mortality rate was high after all.