His old team would be Sasuke, Sakura, and Kakashi. They are the main characters associated with Naruto's early team experiences. In the context of this fanfic where they die, it's likely to have a huge impact on Naruto and the overall story.
It's possible for a 10-year-old to read Naruto comics. However, parents should consider if their child is ready for the action and themes. Some kids at that age handle it fine, while others might find it a bit intense.
Naruto would likely be devastated. His old team was an important part of his early life in the ninja world. He might initially go into a state of shock, unable to believe that they are gone. Then, his grief could turn into anger, vowing to find out who was responsible and make them pay.
Some 'Naruto Old Man' fanfictions could focus on his family life. He might be dealing with a grandchild who has a lot of potential but also a rebellious streak. Naruto, as an old man, tries to guide the young one using his own life experiences. This type of fanfiction can be really heart - warming as it shows the cycle of life and how Naruto's values are passed down.
A third option could be 'Naruto in the Harry Potter Universe'. Here, Naruto enters Hogwarts and the magic world. His unique ninja techniques are contrasted with magic spells. It's really cool to see how Naruto deals with things like the Sorting Hat and the different houses, while also trying to keep his ninja identity a secret.
Well, it could be about Naruto having some sort of special connection with the old man of the mountain. Maybe he discovers some ancient power or knowledge related to it. For example, the old man of the mountain might teach Naruto a unique jutsu or give him a task that will change the course of the ninja world.
You can try websites like Fanfiction.net. It has a huge collection of fanfics, including many old Naruto crossover ones. Just use the search function and type in 'Naruto crossover' to get a list of relevant stories.