Previously you were just moving the goalposts around on where you place the cut-off for age group which is wrong. You need to pick a grouping and stick with it all the way though, but now you've gone completely off the rails. Mark Scheiflele didn’t enter the CHL until he was 17. Connor McDavid entered at 15. Should we be saying Scheifele was 2 years younger at his NHL draft because of this? It doesn’t really make a lot of sense.
When comparing 2 players performance in given league, age group has been shown to make a difference. When they were born within their age group, makes a difference as well, but a smaller one. Either by university year or NHL draft year Connor is in the group 4 years older than Vesey. He's in an older part of his group than Vesey but their age grouping are 4 years apart.