With the best training facilities that were available to me in the academy, I was able to improve my skills faster than anyone else. Though the numbers didn't improve faster, the increase in strength is very high.
As the skill level increases, the rate at which they improve decreases. Increasing a skill level at level 1 by three levels is far easier than increasing a skill level at level 11 by one level.
The difficulty rises as the skill proceeds further. The real problem would be after reaching level 10. It was not just after level 10. At every ten-level interval, the difficulty of improving skill levels increases much more than what it is at a single-level improvement.
If there was no such difficulty, then all those old monsters who have been alive for centuries would have reached level 100 a long time ago. Though it was not made if they have reached level 100, it was said that the difficulty to reach such a level is very high.