It doesn't make sense to say that 22-year olds are garbage as trainees. It must be possible to train up to 24-25 at least, or else how will the soft caps for decent potentials ever be reached. And I do believe they are still trainable.
That wasn't really the point. Right now, I train 20-22 year olds myself. One just can't expect to put in a 20-year old so-so player, and catch up with what top teams have in a season or two. It doesn't work, and it won't work, ever. The top players in the game are usually the product of training 18-year olds with multiple respectable skills for seasons in a row.
"I don't know half of you half as well as I should like; and I like less than half of you half as well as you deserve."