OK Chele, keep in mind that I am NOT the expert on this, but
it seems that your machine was made by the National Sewing Machine Co. in Ill, which closed their doors in 1953..
So I think that you can assume it is at least that old.. and it looks like the machines of that era.
I think probably somewhere between 1924 and 1953.. Not much on this company.. I know that I have one other book, but I cant locate it right this moment.. Ill keep looking..