I created a spreadsheet from the information included in Walter Eliot's book, "Portraits of the Noted Physicians of New York 1750-1900." Then I found other sources including the Journal of the American Medical Association, the New York Times, etc. to fill in the information missing from Walter Eliot's book.
The physicians included in the book were in most cases on the faculty of medical colleges primarily in New York. Some were medical directors of hospitals, while others authored books on a particular area of study. A few invented things of significance in the health care arena of the 19th century.
All of the physicians who obtained an LL. D. degree did so after earning the medical degree. However, all of these doctors continued in their pursuit of medicine after earning the law degree. Most of these doctors earned the law degree twenty years or more after receiving the medical degree. Nearly three quarters of the doctors earned the law degree between 1878 and 1899.
I find it very interesting that so many of these physicians were awarded an LL. D. degree in the 1890s. I do not know why but will see if I can find an explanation. Curiosity is getting the best of me. I am very interested in seeing if practicing physicians during this period who were not affiliated with a teaching school were getting LL. D. degrees as well.
What was the average age of these men when they earned their medical degree? My spreadsheet included the birth year as well as the year in which each earned his M. D. It was easy to add a calculation that provided me with the age of each of the 199 men at the time each received his M. D.
The youngest was 19 years old. Most obtained the medical degree between the ages of 21 and 26. The peak age was from 22 through 24 years. These three ages represents 50% of the doctors in the book. The men who obtained an M. D. age 21 through 26 years of age represent 82% of all the physicians included in the book.
Things have changed from the 19th century to the latter part of the 20th century. I don't have the numbers but I have observations from having worked in the Bio-mathematics Department of the School of Medicine at UCLA in the late 1970s and observing my daughter and her medical school colleagues more recently/ It appears that most doctors receive the M. D. at age 26 years.
The physicians included in the book had areas of specialty for which each was noted. However, from what I have ascertained in my research, formal residencies that the current medical student face before being allowed to practice in a specialized area did not appear to exist during the period covered by the book. Working with a preceptor seems to be the way in which MDs in the 19th century entered specialized practices.