That guy you replied to is obsessed with negging every late birthday for being a "year older", but it's not really how things work. NHL GMs look at "how good is the player, how quickly can he make an NHL team, how good can he become?" All players in a draft year are born within a calendar year of each other (assuming first time eligible) and are looked at on the same sphere. They aren't scouting for future world junior teams, so the "late birthdays" aren't getting dinged. Your original inclination is correct, if a player is 6 months older, then it's a small consideration but a minor one.
This is especially the case when comparing players that have had completely different development paths. If two guys are from the same development path, maybe it's a bit more relevant. To give an example, in the '07 draft, the top two picks as you had it were Patrick Kane and James Van Riemsdyk. Both went to the USNDTP, Kane was a November birthday so he played with the '88 team and was too young to enter the '06 Draft following his team's graduation from the program, so he did a year in London in the OHL for his draft year. JVR was a May birthday so he played with the '89 team and entered the draft following his team's graduation from the program. So you can look at Kane being ahead in that respect, but in terms of which player you take, you're still just looking at those three factors and maybe noting that since they're still pretty young has about 5-6 more months of physical maturity to catch up to.
But when comparing players that are like WHL, USNDTP, NCAA, Swedish Professional, Russian Professional, Swiss Professional, etc. etc., it's not part of the equation at all as there's not a 1 for 1 comparison in any of those.
