Well, you can't really give a specific amount of time...it really depends on your current physical ability, and how much you train per day/week or w/e, and how well/quickly you progress.
So really there is no specific time that you could say..
Depends on the sport you choose, your conditioning, and the time it would take to work up to a competitive state, etc - all unknowns.
Well, it didnt help me much really. I undestand what you said, but I really wanted to hear something like "five years can be enough"
a lot of training daily and a long time