"As" phrases are a bit trickier. Most of the time, "as" is used to compare actions; however, there are times when "as" is used to describe a person at a certain stage of his/her life.
As a young girl, Megan was always happy. --> This means that when Megan was young, she was always happy.
Notice how the above sentence is different from the following sentence (at least the meaning of it):
Like a young girl, Megan was always happy. --> This symbolizes that all young girls are always happy.
This is my 2-cent on how "as" can be used even when not comparing actions.
Please correct me if I'm wrong.
GMAT Club Premium Membership - big benefits and savings