Where's Naka?
Wonder boys: historical rating comparison
I added him, but he is definitely below the rating vs age curve of the other ones, also he is a bit older than the rest of the group (e.g. 8 years older than Rapport, 4 than Caruana).
Basically, Karjakin had a very early chess education (he is Russian Ukranian), and is the best one at a very young age. Carlsen, So and Hou catched up, and this four guys where rated at almost 2600 at 14 years and a half. Then Carlsen had a meteoric rise, while the others (especially Hou) improved more slowly.
Caruana is a different story, since he probably was less into chess at a very young age (he is Italian, no chess tradition. Even if he grew up in USA he was not attending youth chess camps as Karjakin). So his rating was not as high as the other people at a young age. But his rise is steady
In recent years chess has seen the rise of wonder boys. Thanks to great talents, chess globalization, and computer training, youngsters have come to dominate rating lists and chess events.
I did not find any comparison of the best young players at a given age, so I produced a chart of official FIDE Rating vs Days since birth. I have no doubts that the list names include all the best rating (at a young age) in history.
The first chart includes only some players, the second is more extensive but a bit more cahotic. Open the image in a new tab/window of your browser for a higher definition. Kudos to libreoffice developers.