Ok here is the deal, after you do basic, AIT/ and ranger, airborne etc.. is NOT in your contract from initial enlistment it depends on what base you are stationed. Everything is a factor, how high your PT score is, does your post have a RIP program, MOS (infantry is not a problem), do you just want the ranger tab or be in a actual ranger BN? Its not something you just go do, it is something your unit has to get you a school slot for and send you to (assuming its not in your contract). Most units make you do RIP before hand to ensure a greater chance of you actually passing ranger school. IF you manage to get a slot which could take you months to years and you go and pass you will probably just go back to your unit and have a tab....does not make you a ranger, just ranger qualified... It is also possible to be in a ranger BN and not have a tab.
Its a good thing your motivated to do it now but i have seen dozens of people say i want to do this school or that school then after a year they dont care anymore. My suggestion, finish basic and AIT go to your unit, train and get a feel for the army. Work your ass off to get in the best shape you can, NOT bodybuild, sorry to say it but a bodybuilder would be destroyed in ranger school. Any army PT takes endurance and speed, something you cant do if you are super heavy not to mention there are standards for wieght that correspond with hieght and age. I apoligize if i sound negative. Be proud of yourself for lending yourself to a greater cause, best of luck with your army career however long it is, and keep up the working out whether it be bodybuilding, endurance, or strength.