The question is: why is there no Rabbi Akiva nowadays?
I think it has to do with our approach to life and, more specifically, to education.
Nobody wold be encouraged to be shepherd nowadays, it is just not efficient. Sheep should be locked and watched, and you have some kind of more important job to do. If you are a shepherd, the only reason could be your total mental inferiority, in short, you are not good for anything reasonable and productive.
Rabbi Akiva;s insight comes from his observation of droplets of water hitting a rock and slowly eroding it. he realizes that even though he is 40, Torah, like water, can enter his brain and change it. In short, he realizes that he has the capacity to learn. Most grown-ups today will not have an opportunity to make such a discovery. Did you not listen to the lecture on erosion in 6th grade? Why are you staring at a silly rock, who has time for this? In fact, when was the last time you went anywhere near a rock with a water source? And when was the last time your brain produced a new pattern of thought?
Next step: the commitment. You have to go all the way to the beginning. You have to admit that you are not going to be expert. Heck, you will not even be the smartest student in the class. Kids much younger than you will be able to do more. Maybe you will catch up. Maybe you won't. Maybe you will surpass them. But you have to humbly open your mind.
Besides, what would happen today? First of all, there would be a suspicion of pedophilia: why else would a grown-up want to learn with the kids? Then the person would be told to take some placement tests, see where he is, see what he can diagnosed with, see if there is a learning disability to hinder progress. Then he would be told that there are remedial classes available. Then he would be told how much he can realistically expect when starting out at that point in life. He might also be asked repeatedly as to why he decided to change his life's path.
Then there are many years of intense study. The world today does not encourage that kind of study. Sure, there are yeshivas/seminaries, but you are supposed to learn there for a year or two, not more, and even then, it is often an excuse to escape parental control rather than be involved in serious learning. There are adult baalei teshuva programs, but you have to drop everything in order to participate. We simply cannot put life on hold for 24 years. Well, we can't even put our Blackberries down for 5 minutes... Before someone brings up kollel: I doubt that Rabbi Akiva spent those 24 years busily spawning offspring for his wife to take care of on her own.
And afterward? Who would follow a teacher without proper letters of endorsement? There would be talk behind the back: did you know that he was a simpleton till the age of 40? Who knows what horrible influences he had in his life in those years?
In short, while we bemoan the absence of people of Rabbi Akiva's caliber, we do not encourage one to pursue a path which would lead to a development of Rabbi Akiva.