Chiming in a bit late... but enjoying the dialogue so far
The scientific literature suggests that around 4,000-10,000 hours is generally required to gain expertise in a skill. Thats a lot of aikido classes especially, if you factor in that a lot of the time in classes is overhead and not actual practice. At once or even twice a week thats around a 25yr, process assuming active learning can be maintained.
Beyond that and relative to the debate. Early experiences are said to be the most powerful in learning and an opportunity that can be capitilised through intense training at this stage of development.
Blocked learning (repetitive drills, kata?) on the other hand have limited value with emerging expertise in a skill and can infact hinder development whilst breeding a false sense of confidence. You see this most often in the old hands at the dojo just chuggin' it out with the same technique year after year and never taking on anything new within.
best,
dan
(doomed to be a hobbyist but yearning for more)
PS my insights from elite sport if helpful
here