An eligible player will be drafted if he turns at least 18 by September 15th of the draft year but not older than 20 years by December 31st of that same calendar year. Players who turn 19 years old by the draft date are also eligible unless they have already been drafted by an NHL team and are unsigned.
Once drafted, an 18 or 19-year-old may or may not be immediately ready for the NHL, and could continue to play at a lower level, such as juniors or college, to continue their development.
This new rule means 18-year-olds would only be allowed to be selected by NHL teams in the first round going forward, and the rest of the draft, being rounds two to seven, would not be allowed to contain any 18-year-olds. This would be a major change in the NHL if this rule gets approved.