It depends on the specific publisher and the official stance. Sometimes it might be canon, but other times it could be more of a side story or alternate take.
In fanfiction, young Joseph Joestar is often depicted as highly energetic. He's always ready to jump into action, whether it's facing off against an enemy or trying to impress a girl. His brashness is also a common trait. He may rush into things without fully thinking them through, but his quick thinking usually gets him out of trouble.
One popular crossover is with the Fate series. Combining the unique abilities in the Fate universe with Jonathan Joestar's Hamon powers can create really interesting storylines.
There are fan fictions that explore Joseph's early years in more depth. Maybe a story that focuses on his training with Caesar and how that relationship developed further. This could show his growth as a character from a young, brash fighter to a more strategic one.
I'm not entirely sure as I haven't read it in detail. But generally, it might be about the adventures or story of a character named Jorge Joestar with elements related to 'rolling thunder' which could be a metaphor, a special power, or an event in the story.
Well, 'Joseph's Second Chance' is a notable one. It has a well-crafted story where the de-aged Joseph faces new challenges and grows in interesting ways. The author does a great job of maintaining the essence of the character while exploring this new age dynamic.
One popular Jonathan Joestar crossover fanfiction is 'Jonathan Joestar in the World of Harry Potter'. It's really interesting to see how Jonathan's noble and brave character would interact with the magical world of Hogwarts. He might use his Hamon skills in some unique ways within that universe.
Another place to look is FanFiction.net. There are many fans who post their Jonathan Joestar crossover fanfics there. However, the quality may vary, so you might need to read the reviews or summaries first to find the good ones.
One popular young Joseph Joestar fanfiction is 'Joseph's Adventures in Cairo'. It really captures his youthful exuberance and his unique charm. The author does a great job of portraying his relationships with other characters in the series as well.