It depends. You have of course your traditional EMT programs that can run anywhere from 4-6 months. Then there's the accelerated programs that usually run from 2-3 weeks. I don't think anyone here would really recommend the accelerated program if you're new to EMS.
As far as your EMT-I is concerned. You can get it as long as you're 18 years of age by the time you test out for both your practicals as well as written. As most people will tell you, the EMT-I is getting phased out in most places. You really only see them in rural areas. It's rather pointless to go for your EMT-I. Just go straight for your Paramedic. Hope this helps! B)