In my opinion, the market is very broad, dynamic and involves emotions, hence the reason it takes so much time to master.
Trading is not just about what you learn, but it is also about what you experience. Meaning, experience is also part of the refinement of the skills and knowledge you collect. That's what makes trading take time for you to master.
Every trader who starts at the same time, but with a different level of understanding and experience, will affect how quickly their trading develops.
I guess what he said there covers this but this is still more specific. And I bet the experience you mean there is experience in our life, right? It may not only be applicable to some, because you know, some are just lucky to not go on the hard path anymore. It is only interesting or unfair that they are also/usually the ones that have a good grasp on something. There is no rocket science there though but this also boils down to what they eat for example. They might eat healthier than us and the quality of the food is also superb and then they have less stress, so their mind and body are well conditioned to do an activity anytime of the day.