Talent, it´s back! https://www.msu.edu/~ema/HambrickEtAl13.pdf
"The second myth is that it requires at least ten years, or 10,000 hours,
of deliberate practice to reach an elite level of performance..... But the data indicate that there is an enormous amount of variability in deliberate practice—even in elite performers.
One player in Gobet and Campitelli's (2007) chess sample took 26 years of serious involvement in chess to reach a master level, while another player took less than 2 years to reach this level."
This is a nice article, but important to consider that cognitive skill development such as in a chess player is quite different to acquisition of a physical motor skill which might account for the difference. Also must be careful to seperate out individual case studies vs large scale data.
Sometimes though apparent outliers ( could almost segway to the gladwell book here) have a vast background in other , but related activities. Its a whole can of worms. The paper gives a good treatment.
Violin, as a fine motor skill skill is probably a reasonable comparision with aiki. Not that learning violin in my youth seemed to help my aiki in a tangable way- other than appreciation of delayed gratification, discipline etc..
John - sorry for the fuzz just wanted to put a thought out there