"…One may safely assume that every tournament that a junior player plays helps to increase his playing strength. However, the overall level of the young players remains the same after a junior tournament because they all have the same K-factor. But this is an inadequate reflection of their real playing strength.
Players develop particularly rapidly between the age of 10 to 18 but in these years you now only gain Elo points from other players (unlike previously). Some of these rating points come from junior players who quit chess. However, because the playing strength of virtually all junior players increases from the age of 10 to the age of 18 years these junior players mainly gain rating points from adult opponents who “sponsor” the ratings of the juniors. As a result a lot of players ranging from 1000 to 2000 Elo points are underrated which also affected higher Elo levels.
In 2014 the K-factor for juniors was raised to 40. If a junior player (K=40) wins against an adult (K=20) the number of rating points the junior gains is twice as high as the number of rating points the adult loses. The junior player reaches the rating that expresses his playing strength adequately faster but the overall level of the Elo ratings also rises.
Today’s K=40 has the greatest impact when junior players play often against adults because they can show that their playing strength is not much ahead of their rating. But K=40 does not fully compensate the lowering impact the juniors have on the rating of the established players because the juniors gain rating points from players whose playing strength is adequately reflected in their Elo rating and who thus cannot fulfill their Elo expectation against underrated players. How junior players who lose Elo points and quit chess affect the ratings is still unclear.
Arpad Elo (1903-1992) already mentioned the deflationary impact of junior players on the Elo ratings. But if you look at the impact a single game has on the rating of an adult who loses against a junior you see that only a part of the rating loss of the adult is undeserved — depending on how much the junior player is underrated. To illustrate this phenomenon Berthold Plischke gave me the following example:
Junior J (Elo 1600) wins against adult A (also 1600). J wins 40*(1-0.5) = 20 points, A loses 20*(0-0.5) = -10. However, the 10 points A loses are not all undeserved losses: let’s say J had a playing strength of 1700. Then A should have lost 20*(0 - 0.36) = - 7.2. Therefore he only lost about 3 points undeservedly.
In the last two years the Indian Chess Federation had 30% more members! Presumably, most of the new members were juniors. Thus the Indian Chess Federation has a lot of junior players who have only few contacts to players from abroad. As a result the percentage of games in which a junior plays against another junior rises while the percentage of games in which a junior plays against an adult goes down. However, the level of the ratings can only change when players with a different K-factor play against each other. In view of the many Indian junior players the Elo level of Indian juniors will probably rise slower than in Germany.
Germany once also had a large increase of the number of junior players. From 1951-1991 the German Chess Federation increased the number of their members from 25,000 to 90,000. But back then the Elo rating was not introduced or the rating floor was too high for most juniors.
Let’s assume the following: if 100 players who are 30 years old and have an Elo average of 1800 only play against each other in the ten years to come what Elo level will these players have on average when they are 40? And then you take 100 10-year-olds with an Elo average of 1100 and for the next ten years they play only against each other — what an Elo level will they have when they are 20?
Proposals to calculate the Elo rating
Thanks to Berthold Plischke, responsible for controlling the “DWZ ratings” (the German ratings), and an expert in the field. When calculating the “DWZ”, junior players have certain privileges until they are 25 and thus are better integrated into the rating pool. At the age of 25 you should be close to the playing strength you can reach. In 2016, the German Chess Federation introduced another rule to fight the phenomenon of underrated players: if the tournament performance of a player is at least 300 points better than his current DWZ his tournament performance — and not his current DWZ rating — is taken to calculate the new DWZ rating of his opponents…"
en.chessbase.com/post/problems- … or-players