"an elderly Alzheimer's patient"- one of your extracurricular activities (common app)

I need a little help with this essay, I'm not really sure it's relevant or sufficient for the common app. It has a 150 word maximum. Thanks!

One day last summer, I was sitting outside with an elderly Alzheimer's patient named Mary at the nursing home where I volunteered. We talked of silly things like cats and flowers for over an hour in the warm sun. When she felt it was time to go inside, Mary said to me, "I really want to thank you for coming out here to spend time with me. Since I'm not allowed to go out alone and many of the nurses don't have time to go outside, it's a very rare and joyful experience just to go outside for five minutes. You are a lovely young lady, and I hope you realize that even the small things do matter." This was the moment that I realized that my true talent was in serving others because it made me feel good about myself, and I believe that in giving, you also receive.

You may want to include why you were volunteering or if you were volunteering with an organization.

I don't think think the word elderly is necessary in that first sentence, since Alzheimer's and nursing home both suggest it. One way to write well is to make sure you only tell the reader as much as s/he needs to know and no more. Let the reader figure some of it out.

... it's a very rare and joyful experience just to go outside for five minutes. ---- that's terrible! It seems that if a facility is worth paying for it will hire enough employees to make it possible for residents to be outside when they want to be.

This was the moment that I realized that my true talent was in serving others because it made me feel good about myself,----- well, anyone would feel good when thanked.

... and I believe that in giving, you also receive.--- This is a cliche, and it is not worthy of a spot in your essay. It is important to leave the reader with a new idea, something original and intriguing.

:-)