Lowest: 1200 ft, U.S. Army Airborne School, Ft. Benning, GA, but I was on a static line. A freefall jump about 1800 ft emergency exit.
Highest: 21,000 ft. (with oxygen), on the World Record (attempts for the largest freefall formation (at that time we were trying for 300) at Skydive Chicago in Ottawa, IL in 2000.
This is my 20th year of skydiving