The average age of first marriage for women hasn't changed that much over the past hundred years. Since 1890, (I could only find reliable data going back that far), the marrying age of women has mostly remained between 20-22. Only since the 1980's has that the number risen significantly (as of 2011, women in the United States are marrying at 26.9, men at 28.9). The "estimated median age at first marriage" of men has always been between 2-4 years older then their wives.
Marrying young may have been more common in farming communities during this period of American history, but 16 was even young by that standard.