[acsrp38]

Depending — it can take 10 to 20 years — usually about 10 or 12

[Lobato1]

Now it seems that the guy was an MD & they usually enter with the grade of captain.

Major could have taken him some 5 more years from the time he entered the service.

Best Regards
Lobato1

[Goreknowshowtocheat]

Most doctors are automatic Captains in Army. Some, depending on experience, can be Majors coming out of civilian life.