This tells a very important story about the NHL draft. Historically, teams value 1st-year draft eligible players more because they have a longer time frame before their potential is set. They are considered to be more malleable, with more room to grow. While this may be the case, there are a couple of counterarguments that suggest this mentality is flawed.
They Spend Less Time Developing With Our Team...
A common thought process for NHL teams is that if you draft a 19-20-year-old, they will have spent less time under the tutelage of the organization, therefore losing development time that they could have had if they were a 1st-year draft-eligible player. This is a true statement, and yet at the same time, it really has little to no significance. Unless a player is drafted in the top 5 of the NHL draft (and even this is changing), they are highly unlikely to play the following season. This means they are going to play in a developmental league, such as major junior in Canada, NCAA Division I hockey, professional hockey in Europe, etc.
Consequentially, they will not be surrounded by the NHL staff that they consider to be essential for the development of their players. NHL teams have to rely on other teams to serve as a developmental pathway for their players. Even if they are playing within the NHL system, they will likely be playing for their AHL affiliate, which will be located in a different city, and facility, and will be surrounded by a different staff.
NHL teams value being able to watch over their players throughout the year. They have calls and check-ins with their players. They also likely have conversations with the coaches and management staff for the developmental teams their prospects play for. Due to this ideology that watching from afar has an effect on how their players develop, getting the extra year is important to them.
The argument that counters this ideology is: what does it matter if they weren't part of your organization at 18 years old? If they are going to end up at the exact same spot (in a development league), why does it matter?
The answer is: it does not matter. NHL teams do not have control over these developmental leagues, and as a result, they do not have control over how their players are developed with these teams. These teams will use the NHL prospects for the assets that they are, to generate success for their team. Yes, these teams do care about the development of their players, but their main focus is to utilize their best players to win. Whether that means an NHL draftee gets over-played so that they can make playoffs, or if their NHL asset is not performing so they push them down the lineup for an older player to get more minutes.
In summary, NHL teams should not discount over-age players for this reason, because they are playing in the leagues that they are playing in regardless of being drafted.
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
The Older You Are, The More Set You Are As A Player...
There is this large misconception that by taking a 19 or 20-year-old player, you're taking a player who is closer to their maximum potential. Therefore, drafting an 18-year-old gives you a longer runway to develop and mould them into a desirable player. While conceptually, this rationale follows physiological and psychological theories of development, there is another perspective that supports the over-ager analysis that I conducted.
The argument that counters this ideology: why do NHL teams rush to pick 18-year-olds who are less of a finished product when there are over-agers who are marginally older with a more secure potential?
Instead of looking at over-agers as players with less room to grow in their potential, I would argue that, in reality, scouts get a better idea of what these players can become. With an additional year of viewing the player, their tendencies and abilities, scouts can start to form who that player will be. Given they will be in a developmental league regardless (see argument above for rationale), there is no reason to hinder someone's relevance as a prospect because they are only a few months older than their linemate. From my Over-Ager Analysis, there is evidence that supports this. Because teams are typically more likely to make a successful pick on the over-age draftees between rounds 3-7, this suggests that knowing more about the player from watching them for an extra year or two is the lead cause of the more successful draft picks.
Furthermore, the concept of age that has been implemented in the NHL draft has proven to be relatively inconsequential. At 15 years old, the physiological gap between certain players is obvious. Some individuals have not yet reached puberty or are just in the initial stages of the biological and physiological transformations that come with puberty, while others are closer to being fully grown adults. At this stage in life, 3 months could have a massive influence on a player's ability. But once they reach 18, for the vast majority of NHL quality talent (there are always exceptions), the physiological gap has closed. While players are not fully grown (either height or weight will likely change by the time they reach professional hockey), there are far fewer players whose entire physiology changes after several months. Knowing this, NHL teams should focus less on the age of the player, and determine the best player available. This concept of taking the 'best player available' is something that is discussed a lot in the NHL draft, particularly in relation to the 1st round. I believe that this strategy can be implemented when evaluating over-agers.