Complex sentence: At the age of 20, he finished fourth in the mile and second in the 4 miles at the 1920 AAA Championships, and was invited to run in the 1920 Olympic 5K, but was unable to accept.
Split into simpler sentences: At the age of 20, he finished fourth in the mile and second in the 4 miles at the 1920 AAA Championships. He was invited to run in the 1920 Olympic 5K, but was unable to accept.