On the issue of how much time it takes for a PhD in the USA:
Many variables involved: University, Department, Thesis Advisor, Thesis Committee, Thesis topic choice.
I finished a PhD in Physics at a major mid-western state university in four years. I matriculated after my BS degree in Septembger 1967 and was granted my PhD degree in October 1971. One of my starting classmates finished in May of 1971, five months before me. Another of my starting classmates took 8 years to finish. The basic requirements for the degree could be completed in three years time if you could take a full credit load every semester and during the summer half-semester as well. the main variable for my physics fellow students was thesis topic choice and thesis advisor. Some choose a poor thesis topic that is difficult to bring to a successful conclusion. Some thesis advisors want more years of coolie labor out of their students than others. My cousin had gone to this same university six years before I did. He coached me in (1) choosing a thesis advisor by looking at how long the advisor's students took to finish (pick a quick one!) and (2) pick a thesis topic that has as much definitiveness as possible in that advisor's field of study.
My cousin finished his PhD in three years and was 21 years old when he finished. He was the son of a Christian missionary in India and went to a school for foreigners in India: Kodaikanal International School. This school let him graduate from "high school" at the age of 15. He came to the USA and went to a college affiliated with his father's (my uncle's) church. They let him graduate from college in three years, i.e. at age 18. He then went to the same big midwestern university that I later went to and earned a PhD in Organic Chemistry in 3.5 years. He went to work in the research laboratories of DuPont at age 21 as a research scientist. After four years at DuPont he was offered a university professorship and was a tenured faculty member by age 27. So, there are some very quick PhD's and many slow ones. Quick PhDs come about because of superior planning (by the student) or luck (a thesis topic that "clicks" from the word "go").
Im glad to see we have one on this forum who is from MIT. MIT is the highest ranked engineering institute/ university of the world for engineering studies. Did you get scholarship or paying for, how much did you score in GRE? 
. But it is still not bad if we see even IIT Bombay at 49. But I can see that UTS is still among top 20 engineering institutes in world if we check 5 Star label also. 
