Nagato was 34 years old when he died, but Kakashi was 29. This would set them at most, only 5 years apart. How can this be when Nagato was 7 when Jiraiya started training him. Later, Jiraiya started training Minato (who was a kid at that time). Then, Minato was an adult when Kakashi became jonin at 9. So, Nagato should be older than Minato. He should also be at least a generation older than Kakashi.
Minato died at the age of 24. If he were to survive, he would have been 36 in Part 1, and 39 in Part 2.
In Part 2, Nagato's age is confirmed to be 35, in the databooks.
This means there's a 4 year age difference between Minato and Nagato, where Minato is elder.
Kakashi's age was about 29-31 in Part 2, confirming that he's younger than Nagato by 4-6 years.
First of all we need to remember that when Obito approached Yahiko and Nagato (there age was around 15). At that time Minato was a Jounin and leader of Kakashi and Rin. So there is no point that Minato was younger than Nagato
It's pretty easy to explain. It doesn't make sense that's the eplamation. In the manga it's very much Portraits as if jiraiya Trained Minato after nagato. This makes no sense but that's the way it's portrayed. Even more so because from the evidence that we have from manga and databooks, it's pretty clear that nagatos Training still happened in the SECOND shinobi war.
We can deduce that because the thirdly was when kakashi was 13/14 of course it might have rages on before that But for nagato to witness it as a young child it must have lastet over ten years. Which would else mean that sakumo hate would have fought in this war which he as far as we know didn't.
We also know that dan died in the second war and after das death tsunade leaves the Village. Not only is she still There when jiraiya First met the Ame Kids, But she is still There mire than three years after when they get the message that the Kids died. So at that point we're still in the second war. Nagato and Minato are too close in age for it to make sense. Even less so because we know he didnt go Straight from training one child to the other.
It would Maybe make sense if Minato came First But from the way it is portrayed it seemed like nagato was First. Even if I dont like the whole 'putting jiraiyas time line together' even less when looking at it from a political perspective. The only way it Made some sense were if jiraiya went Straight from one Student to the other. That Would mean he had a still rather young Team that he just left hanging for three years to train the orphans.
Even more so he left konoha in a time of War for three whole years without repercussions and is still considered the Best candidate for hokage by just about anybody.