Basically only when it comes to national team.
If you go by calender year it will give the early born a big advandge, much more then if you would go with draft year. The late born will missout a summer training etc, and you know a lot can happen then at that age. Many young player come out of the summer training as a new player.
18 out of the 20 best historically U17 season in superelit, was born, "early". The 2 born late was the sedins. Look at best U18 season in shl, 18 out of 20 best early born, the 2 late born, Sedin and A Larsson, while many of the early born was also here medicore players. Look at allsvenskan, best U18 season there, 17 out of 20 best is born early, among the 3 late, you find for example Pettersson.
Now you can say that more are born on the right side of the year, so it is expected that there are more, but still. Plus it is basically only special talents among the late born that break into there, while among the early born it is very mixed. Take out special talents like sedins, and it is almost 100% early born.
Do we see that older get the same advandage when you compare in draft year instead of calender year? I would say no, not even close. This is their working year, that is the most relevant. That is when the hockey year starts, no matter what is says on the calender.
When it comes to UXX national team it should go by calender year, because it is easier to understand and tradition, but it is maybe not the most fair.