This looks like it might be a good place to start.This particular census was taken 01/15/1920, with information "as of 01/01/1920".Look at the age of the twins at the bottom of the list.
1920 United States Federal Census
Name: Edward Kirby [Edward Kerley] Age: 41 Birth Year: abt 1879 Birthplace: Tennessee Home in 1920: Grassycone, Cumberland, Tennessee Race: White Gender: Male Relation to Head of House: Head Marital Status: Married Spouse's Name: Eva Kirby Father's Birthplace: Tennessee Mother's Birthplace: Tennessee Home owned: Rent Able to Read: Yes Able to Write: Yes Neighbors: View others on page Household Members: Name Age Edward Kirby 41 Eva Kirby 37 Lena Kirby 14 Lennice Kirby 12 Lenard Kirby 10 Lawn Kirby 3 Frank Kirby 0 [6/12] Elma Kirby 0 [6/12]
Ancestry.com. 1920 United States Federal Census [database on-line]. Provo, UT, USA: Ancestry.com Operations Inc, 2010. Images reproduced by FamilySearch. Original data: Fourteenth Census of the United States, 1920. (NARA microfilm publication T625, 2076 rolls). Records of the Bureau of the Census, Record Group 29. National Archives, Washington, D.C. For details on the contents of the film numbers, visit the following NARA web page: NARA. Note: Enumeration Districts 819-839 are on roll 323 (Chicago City).
Description: This database is an index to individuals enumerated in the 1920 United States Federal Census, the Fourteenth Census of the United States. It includes all states and territories, as well as Military and Naval Forces, the Virgin Islands, Puerto Rico, American Samoa, Guam, and the Panama Canal Zone. The census provides many details about individuals and families including: name, gender, age, birthplace, year of immigration, mother tongue, and parents’ birthplaces. In addition, the names of those listed on the population schedule are linked to actual images of the 1920 Federal Census.