I was in the 7th grade.
One summer afternoon I was lying in the hammock in our back yard, when a small dot appeared on the horizon, flying in a straight line roughly from North to South.
I was extremely interested in airplanes, being able to identify everything flown by the USAF, and being familiar with the speeds they can attain.
This was at the time of the first operational jets, and it was 15 to 30 times faster than a jet.
It only took about 8 to 10 seconds to traverse the entire sky, horizon to horizon, a distance I estimated at 25 miles, more or less.
The speed must have been 10,000 to 15,000 mph.
I had excellent vision at that time, being a little farsighted.
The craft was too high to be able to determine shape, but there was no doubt as to the fact that it was real, and that it was fast!