I confess I was rather shocked to hear this- in my experience, adults who make an effort to play a large number of games at the expense of studying develop a playing style in which many common mistakes become solidified. I have visited dozens of Go clubs and witnessed hundreds of adults who play common mistakes over the years.
I have great respect for these pros- after all, they are some of the best in the world- but I could not understand why they said this. So I decided to look into their biographies and playing experience. Some relevant facts I discovered:
1. Both Ootake and Iyama had wonderful Go teachers when they were kids.
2. They began learning Go when they were young, so they learned everything very quickly (young children often learn something once and never forget).
3. In addition, they also happened to be extremely talented Go players.
When Ootake was a child, he went to a Go club near his house and played with many adults. In this Go club, there were some strong players. When I read his biography, I can infer that those strong players had a properly training, so they knew advanced tesuji and techniques. He also had a 5dan Go teacher (at that time, the rank of 5dan was equivalent to what we would today consider 7dan or higher). Under his tutelage, Otaka improved miraculously. Later on, he became an apprentice of Kitani Minoru 9dan.
(It is important to have a good teacher and / or to be surrounded by players who have been well trained. As far as I know, in a majority of Go clubs in Tokyo many of the strong players never have proper training, so they don’t know tesuji or good shapes. But their styles still work because their opponents are also not properly trained.)
When Ootake started living in Kitani Minoru’s house, there were already many talented Go prodigies who were pros and insei (Go apprentices), living in the house. Ootake played stronger players all the time.
Iyama also had a good Go teacher. His grandfather was a 6dan amateur and taught him for a year. Iyama stared playing Go at the age of 5. He became 5 kyu in half year and then became 3dan in another half year. It appears to be like the grandfather had a proper training, so he could teach his grandson well.
Then, he was introduced to Ishii Kunio 9dan pro who entered the Meijin and Honinbo Leagues. About 95% of the Japanese pros cannot enter these leagues. Some pros enter it only once. So the fact that he entered three leagues prove that he was one of the top pros when he started teaching Iyama.
Ishii 9dan taught Iyama twice a week. At first he played a six-stone handicap games and gave the commentary over the phone. Ishi continued to teach Iayam even after he became a pro every week.
Also another pro, Kenmochi Jyo 7dan, played with Iyama once a week before Iyama was a child. He also went to Kenmochi’s house in summer and winter vacations and played with him, Takao Shinji pro, who later became Honinbo, and Akiyama Shinji pro, who later becamse 9dan.
One day Iyama also joined the late Fujisawa Hideyuki Go camp and played many games with top players.
Ootake and Iyama were prodigies, had great Go teachers who played a large number of games and reviewed their games.
But not all pros had this kind of wonderful environment.
For example, Fukui Masaaki 9dan did not have a Go teacher when he was a child. He had only famous Honinbo Dosaku game collections. Dosaku was once the strongest player during the Samurai period. Fukui played those games so many times that he eventually memorized all the games.
I was once an assistant of Sensei Fukui’s class and taught with him for three years. During that time, I never heard him say “amateurs should play as many games as possible”. He seemed to give advice differently to a different student.
Consequently, pros’ advice has a lot to do with their personal backgrounds.
Also the advice of Ootake’s and Iyama’s may not apply to adults becuase most amateur adult Go players have different situations.
1. Most adults don't have very good Go teachers. So they may study for years without learning proper tesuji, shape, joseki, etc.
2. When adults learn tesuji, shape, joseki in a Go class, they have a hard time remembering it. (Kids who are dan level can learn shapes, tesuji, patterns and retain this knowledge for a long time.)
3. Most adults are not Go prodigies like Ootake or Iyama.
4. Most adults started learning Go when they were an adult, not a 5-year-old.
In my experience it takes adults a certain amount of time to learn just one tesuji; it may take up to a month. That's not what happened with Ootake or Iyama. They could learn one tesuji and begin using it in their games immediately, and they would never forget it.
This is not to say that all children are natural Go players. There are many children who are not as talented as Ootake or Iyama; quite a few stop playing Go because they cannot
improve quickly.
Also without a Go teacher who teaches and cares about kids, it may not be easy to improve or enjoy playing Go. The other day I had an email from Mimura Tomoyasu 9dan, who has entered the Meijin and Honinbo Leagues many times. He runs a Go school for children. Quite a few kyu players quite because there aren’t a Go teacher there. All the pros are busy teaching dan players.
In conclusion pros tend to give advice based on their experiences. But that may not be applicable to anyone.
Please also read a related topic: http://kazsensei.seesaa.net/article/409180298.html
. You should build a strong foundation of go.
. To do so, you have to do drills or study over and over again.
. When you play a game, you should review it and try to
. The continuation of your Go study or practice will lead to 
. You should improve your concentration.
with somebody, then you may
I'm sorry if I sound like I'm preaching. 
