If you clicked this hoping there would be an answer to the question posed in the title, sorry – no dice. No idea how long it took these guys to master the trick shots they’re showing off, but if I had to guess it would be over or under a million years. Maybe a little more, maybe a little less, but that answer is unsatisfying enough that you probably don’t care about its accuracy.
Then again, you DID click on a tennis trick shot video, so you’re either very bored (meaning that you don’t care) or a trick shot enthusiast (meaning that you do care, but too bad I still don’t have an answer for you). Doesn’t matter which it is, because the answer is still A MYSTERY.