I was lifting weights for over a year before I even considered doing a pull-up.  I had to do assisted ones for about two months before I could do a single genuine pullup.    But going from being able to do one to doing ten in a row took only 10 days, or so. These days I alternate weights with body-weight (lsits, pullups, dips), as well as climbing for core-strength.  But I'd guess an average person can't do a pullup without at least some practice.  Not a year, but some.