Well, Naruto might try to give his younger self some advice. Maybe he'd tell him to train harder or to be more understanding of Sasuke earlier. It could be a really interesting scenario where the older Naruto tries to prevent some of the bad things that happened in his past from occurring again.
Friendship might be a theme. The older Naruto could emphasize to his younger self the importance of his friends, like Sasuke, Sakura, and Kakashi. Also, the theme of destiny. The older Naruto can tell his younger self that he has a great destiny ahead and should keep striving for it. And it could be about forgiveness too, as Naruto has had to forgive many of his enemies throughout his journey.
In a fanfiction scenario where Naruto meets his younger self, it would be a very unique situation. Naruto might show his younger self some of the new jutsus he's mastered, like the Rasengan variations. His younger self would be eager to learn from him. Also, Naruto could talk to his younger self about his dreams and how he's still holding on to them, even after all the difficulties. This meeting could potentially change the course of his younger self's life, as he could be more determined to reach his goals faster with the knowledge of his future self.
If Naruto is sealed in his younger self in a fanfic, it could be chaotic. His chakra control might go haywire as his younger body tries to adapt to the sealed future self. The village elders might notice something strange and try to investigate. His training with Iruka Sensei could take a whole new turn as he might show advanced skills too early. This could also have an impact on the Nine - Tails within him. The Nine - Tails might react differently to this new situation, perhaps becoming more or less aggressive depending on how the seal affects Naruto's mental state.
In this fanfic, Naruto might teach his younger self some advanced jutsu. For example, he could show the younger Naruto how to better control the chakra for Rasengan at an earlier stage. This would make the younger Naruto stronger faster in the story.
In this fanfic, Naruto might use his time - traveling jutsu accidentally. He could then see his younger self in a dangerous situation, like being attacked by a powerful enemy. So, he jumps in to save him, using all his advanced skills and knowledge. Maybe he also gives some important advice to his younger self to avoid future mistakes.
Well, in such a fanfic, Naruto might initially be confused. He could start comparing his own life experiences with those of his alternate self. Maybe they would exchange stories about their training, friends, and enemies.
His older self might become more nostalgic. Meeting his younger self would remind him of his more innocent days. He could become a bit more carefree again, like he was when he was younger.
The story could develop in many ways. For one, Naruto's friends might notice his sudden change in behavior. He might seem more mature or have knowledge that he shouldn't have at his young age. This could lead to some interesting conversations and misunderstandings. Also, the ninja academy days could be completely different. He could potentially skip some levels of training or teach his classmates new techniques. The story could also focus on how he tries to keep his sealed self a secret from those who might try to take advantage of it.
One possible thing that could happen is that Naruto could teach his younger self some advanced jutsu. For example, he might show the younger Naruto how to better control the Nine - Tails' chakra earlier. This would give the younger Naruto a significant power boost and change the way he approaches battles in his early days.