Observed small gray disk.

My mother asked me to hoe her flower garden after dinner.  So, as a 14 year old boy, I went out after dinner and began hoeing my mother's flower garden.  Our home sat on a lot that was 80 x 234 ft.  This garden sat at the 120 ft mark.  As I was hoeing I was looking north.  However, I turned around. I saw a disk shaped object face on.
This disk was about 15 inches in diameter.  It was about 8 ft above the ground and was just beyond the rear property line.  So this disk was about 120 feet away from me.  The disk was a dull gray in color.  I saw no markings or lights.  It made no sound.  The sky was clear and the temperature was pleasant.  I watched this disk for about 5 minutes.  Then the object began to recede slowly.  It became smaller and smaller until I could not see it any more.  
Total observing time was about 10 minutes.
Source of report indicates that the date is approximate.  PD