Jason is raised in the wilderness by Chiron the centaur, until the budding hero is old enough to return to his hometown of Iolcus to claim his birthright. This transition from the country to the city was probably a major culture shock for young Jason. Imagine if you'd spent your entire life hanging out in the woods, and then one day walked into New York City. Your mind would probably be blown. We're guessing it must have been the same way for Jason.
The convention of heroes growing up or spending some part of their lives in the wilderness happens a lot in world mythology. It seems to get across the idea that spending time away from civilization in some way purifies a hero, making him ready to go out and do great things.
The myths of Jason all take place a super long time ago. Even to the old guys who first wrote down Jason's story, he was a legendary hero from the distant past. Sometimes the era that Jason and his fellow heroes lived in is called the Heroic Age. Back in these days, the heroes were the sons of gods and the world was crammed with villains and nasty beasts that really needed slaying.
It's important to think about the fact that even to ancient Greeks, Jason was an ancient figure. It's pretty likely that the fact that heroes in the stories lived so long ago added to the highly fantastical and exaggerated nature of the tales. If a rumor gets passed around school long enough, it gets totally blown out of proportion, right? Well, it's the same way with myths. Someone tells another person about a cool thing somebody did, then after a thousand years of people retelling the story, it gets totally off the hook.