How long will it take practice for me to achieve 4-5 octave voice?

Vocal range in modal register depends on the size of your vocal chords and it's fixed. Most of the times, it can't be more that 3 octaves.

Well I'll be perfectly honest with you, you cannot train it. It is physically not possible. You can be born with a voice that is able to do that and then just develop it, but unless you are a brilliant voice talent like Bobby McFerrin, Prince or Marriah Carrey, then there is physically no way, how to train your voice to have a range of 4-5 octaves. This is something that is gift of God or the Flying Spaghetti Monster of whoever. Now what you can do is improve your range, that is of course possible, but not by much. The simplest way is to get a vocal teacher. You need to get a great singing technique. I don't know how good a singer you already are, so I'll say this - if you want to have a big range, you'll need an impeccable technique, so the vocal chords can handle it. So get a teacher so he can teach you the right way to sing precisely. Then you just need to train and sing and sing. Get some exercises, either on cd or download some. Best of course is if you have a piano or something, so you can play along. Usually if you have a talented voice, a good teacher, a lot of patience and time on your hands and you train a few hours a day (every day) then you'll see improvement in about a year, real improvement in technique and overall sound in up to two years. From there it is a continuous training/singing trip. You'll need to continue training and singing for as long as you want to sing. Vocal chords are muscles, so they can be trained, but if you don't use them, they'll get soft again and forget everything. So if you really wanna go for it, do it, but expect it to eat a lot of your time, if you really want serious improvement. It won't be 5 octaves, but you can achieve a lot, if you commit to it.

Sorry to break it to you kid, but that varies from person to person whether or not it's possible and takes years to develop. You honestly don't need that much, 3 octaves is good for most songs out in the world today. Everyone has approximately 3 octaves.