I've found a fair number of formulas online which let me convert birthdate into decimal age in years but I can't find something that converts, for instance, 1.0 into 04-Nov-2011.

Any help would be much appreciated.

EDIT:

Here is an example: I currently have data which has been derived from converting dates of birth (i.e. 04/08/07) to "decimal years" (i.e. 3.75). The original DOB data has since been deleted. I would like to recalculate the DOB from the remaining decimal number which represents years (i.e. What is the date of birth of someone who is 3.75 years old?)