In Part 6 of JoJo’s Bizarre Adventure, titled “Stone Ocean,” Koichi Hirose does not make an appearance as a main character. Therefore, it is not explicitly stated how old he is during this part of the series. However, based on his age in previous parts, we can make an educated guess about his age.
Koichi is first introduced in Part 4, “Diamond is Unbreakable,” where he is shown to be a 15-year-old high school student. Part 6 takes place approximately 10 years after the events of Part 4, so if we assume that Koichi’s age remains the same, he would be around 25 years old in Part 6.
However, it’s important to note that the passage of time between parts in JoJo’s Bizarre Adventure can be somewhat ambiguous. The timeline is not always explicitly stated, and there are occasional discrepancies. So, while it’s reasonable to assume that Koichi would be around 25 in Part 6, it’s also possible that the timeline differs slightly.
Additionally, it’s worth mentioning that Koichi’s absence in Part 6 suggests that he may not play a significant role in the story during this part. This could be due to various reasons, such as his character arc being resolved in previous parts or the focus of the narrative shifting to other characters. Without further details, it’s difficult to determine the exact circumstances surrounding Koichi’s absence.
While we can estimate Koichi’s age in Part 6 to be around 25 based on his age in previous parts, it’s important to remember that the exact timeline and character involvement may vary in JoJo’s Bizarre Adventure.