it is most common for eevees to evolve in their mid teens to early twenties, as that is when they will be exposed to the most stimuli that may trigger an evolution.

eevees that reside in rural eras generally evolve earlier than those in urban areas due to the higher likelihood of them encountering scenarios in which they would evolve.

generally speaking there are four ways that one may evolve; intentionally, typically, by chance and inadvertently.

eevees that evolve intentionally will partake in specific habits that expose them to stimuli which may trigger an evolution.

eevees that evolve typically generally will have partaken in habits that may trigger evolution normally, not having sought out to evolve.

eevees that evolve by chance may have encountered stimuli to evolve at a significant time in their lives which caused them to evolve.

eevees that evolve inadvertently may have experienced some significant event or feeling tied to the trigger of their evolution