The excerpt uses explicit details in the following way: it provides a physical description of Sarah Penn (small woman, short waist, gray hair, mild forehead, downward lines about her nose and mouth). All of it is explicit, since there is no room for interpretation, it is what it is. In other words, such details are concrete ones, since they are physical and nothing else.
As for implicit details, we can find them in a figure of speech (a hypallage, which uses an adjective or participle to describe a noun other than the person or thing it is in fact describing): we learn Sarah Penn's forehead was benevolent, that is, it showed her benevolence (an implicit detail, since it was Sarah, and not her forehead, that was benevolent). It is a trait which implicitly tells something about the character's personality. There is also the description of meek downward lines about her nose and mouth. Again, a hypallage which implicitly tells us something about the character: it is Sarah who is gentle and humble, and not the lines about her nose and mouth.
