I can only say that I am "almost" sure. I was born in June 1948 and his age is listed as 47 years old on my birth cetificate. I never asked my mother much about my biological father before she died and I didn't even know my stepfather was not my biological father until I was 16 years old and saw my birth certificate for the first time when I got my drivers license. One of the few things she remembered about him was his birthday, September 14. But I cannot be absolutely sure that he was not 6 months or even a year older.
The info you gave me is all I have and is a real good start. How many Arthur Jacksons can there be who was born in Macoupin County Illinois in 1900? Many thanks!