1. Michael’s heart attack was a real turning point in his life. He changed his reckless ways and began eating better, exercising more, and relaxing more.
2. Anna had to decide whether she would pursue her career in dance or go into business. She realized that she could not do both. This decision would be a major turning point in her life.

Similar to: make or break. The expression suggests a fork in the road where one must turn in one direction or the other, depending on which path one chooses.