George S. Ledyard
I think it depends on the student... The young 20 something boys who want to kick ass are off doing MMA these days anyway. I don't see them in Aikido any more. The older more mature students we get actually like the training. They get a lot of wins, it isn't too stressful, and it's sophisticated which appeals to these very intelligent folks. The hard part is getting them to want to up the intensity as they get better. The safety required to train properly can become something they get attached to. Especially as most of my students these days are already in their thirties... We just aren't getting the youngsters who can train their brains out physically the way we did. So what I find is that I have a bunch of folks who are functioning at a very high technical level compared to what one might generally see around but they can't necessarily do their stuff at high intensity under great pressure. It's a hard balance to find.
There are exceptions of course (Horikawa and Sagawa started training quite young under the guidance of their fathers), but I believe a vast majority of early Aiki practicioners were well into their thirties and forties when they began training.