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.