By shapeshifter I believe that he his speaking about the ranger archetype from the APG in which he would be able to take on the characteristics of an animal aspect in exchange for a normal ranger's favored terrain.
As for your question, I believe that as long as you have the prereqs for the feat you would be fine in taking it. The only thing about waiting until 10th level as a ranger is that you would get the feat for free without needing the prereqs.
*edited for spelling issues
