One possible plotline could be that Harry discovers a hidden magical world outside of Hogwarts. Maybe he stumbles upon a group of rogue wizards who teach him their own brand of magic, away from the traditional Hogwarts curriculum.
The main antagonists could be those who don't want Harry to receive a proper Hogwarts education. Maybe some dark wizards who fear that Harry will become too powerful if he goes through the Hogwarts training. So, they plot to keep him away from Hogwarts.
One possibility could be that Harry discovers he has some other magical destiny outside of Hogwarts. Maybe he is taken in by a different group of wizards who teach him their own brand of magic in a hidden location. They might believe Hogwarts is too mainstream or that Harry has a special power that needs to be nurtured away from the school.
Ron could also be important. He might be torn between his loyalty to Hogwarts and his friendship with Harry. Eventually, he could choose to leave Hogwarts to be with Harry, bringing his Weasley family charm and his own brand of magic to the group. The Weasley twins might also get involved, providing some much - needed humor and their unique magical inventions.
Well, perhaps in 'harry goes to hogwarts later fanfiction', he could form new friendships. He might meet students from different backgrounds or even different magical cultures, which would bring a whole new dynamic to his Hogwarts experience. He could also discover new magical abilities or spells that were previously unknown to him, which would help him in his adventures at Hogwarts.
Maybe he meets an old Canadian witch who has a lot of wisdom about a certain type of magic that is rare in the UK. She could give Harry some valuable advice or a magical item that helps him later at Hogwarts.
One possibility is that Harry grows up in the Muggle world completely unaware of his wizarding heritage. He might lead a normal life, going to a regular school, making Muggle friends, and having no idea about the magical world that could have been his. Maybe he has a natural aptitude for something like martial arts or a particular academic subject that in the wizarding world would be replaced by magic.
Well, he might discover some unique magical creatures in Canada that are different from those in the UK. Maybe he meets a friendly Canadian wizard who teaches him a special spell.
One possibility is that Harry's late arrival at Hogwarts could change the dynamics of the relationships he forms. For instance, instead of being in the same boat as the first - years from the start, he might end up befriending some older students who take him under their wing. Also, his late start could mean that he discovers parts of Hogwarts that others haven't yet, like secret passages or rooms that are only accessible to those who arrive late or are in a certain situation.