Imputable is not a very common word. I will go out on a limb and say that the average English speaker would not understand the word. It is not normally used when talking about characteristics of people.
We would say attributable in normal context when talking about people.
I fully agree with Jacinta - one rarely sees "imputable" used (conversely to "impute to"). Where I see it most often is in accounting where costs may be imputable or not (i.e. charged). Another good synonym in addition to "attribute" is "ascribe".