Big Cheese,
I think you could stand to focus a little more on your motivations and less on your qualifications, but this is one of the rare situations that I think you are fine as is. DEFINITELY get it under 400, but I'm about to recommend about 70 words for deletion.
I have looked fire in the eye and did not flinch; I was only 18 years old.
Your tenses are confused.
Easiest fix is to delete "have," but I would put "I was..." in front: "I was only 18 years old when I looked..."
While my peers were focusing on a single goal such as studying for the next test
1) Lies
2) No good comes from this (portion of the) sentence
I was not only academically preparing myself at West Chester University, but I was also developing my firefighting skills in a volunteer fire department at age 17.
Again, I would put the age in front. [Although I wouldn't use it at all, because it sounds weird in front but if you put it in front your essay's chronology gets weird.
However, my interest in firefighting and adventurous drive ultimately focused my attention to begin a career as a professional firefighter in the U.S. Forest Service.
1) Delete
2) Yuck
In my first two years as a firefighter with the U.S. Forest Service, I developed professional skills involved with incident command and resource management.
1) I would delete
2) I don't know what the right phraseology is, but this
can't be it. If it is, write something else.
This helped me obtain a job with the Philadelphia Fire Department, where as a 20 year old novice firefighter, I quickly earned the respect and trust of the veteran crew members with 20-30 years of experience.
1) Should be "these skills" still, yes?
2) I would go with something more like, "many years," "over twenty years," or "as many as 30 years."
One of the most important lessons I learned working for the Silver City Hotshots is that no matter how hard ... digging a mile long fire line at night in Yosemite National Park, I will finish eventually, knowing I gave everything I had and refused to give up.
Needs to be fixed.
Instead of continually thinking about the difficulty of the mission, I preferred to think about the gratification of completing the mission after giving 110% of my effort.
There's nothing particularly necessary about this sentence.
Like my grandfather, his three brothers, my uncle, and my sister, who all served in the U.S. military, I have the necessary strength of character, esprit de corps, and the leadership capability that is necessary to serve my country in the United States Navy.
Esprit de corps is, I'm fairly confident, a quality of the group, not of any individual. You wouldn't say, "I have the morale that is necessary to be an officer."
By choosing me as an officer candidate, you will select a seasoned, hard working, and trustworthy candidate who has proven teamwork experience and an ability to function in the most challenging circumstances.
No good comes from this.