Has anyone noticed this?

So if we think about this logically, 2 seasons would be 1 year apart, because they’re all British seasons, so there can only be 1 season/summer. So season 6 would realistically be 3 years apart from season 9. However, in season 6, Hamish (sorry, he’s my example, cuz he was my main focus in season 9) is apparently 28, while in season 9, he’s 29 years old😅 or am I missing something?🤣