Which of the following is the correct way to punctuate this statement?
A. At age ten; Jeff knew he wanted to be a doctor; at age thirty: he was finishing medical school.
B. At age ten Jeff knew he wanted to be a doctor: at age thirty; he was finishing medical school.
C. At age ten Jeff knew he wanted to be a doctor at age thirty he was finishing medical school.
D. At age ten, Jeff knew he wanted to be a doctor; at age thirty, he was finishing medical school.