Broccoli is considered over mature when:

Broccoli is considered over mature when four or more flowers are open. This is because the ideal time to harvest broccoli is when the buds are tightly closed and before any flowers begin to open. Once the flowers start to bloom, it indicates that the plant has passed its peak harvest time, leading to a decline in quality and flavor. This stage is undesirable for commercial growers and consumers alike, as opened flowers typically mean the texture is changing, and the broccoli is becoming tougher and less palatable.

The other options do relate to the maturity of broccoli but do not specifically indicate that it is over mature. Yellowing may suggest that the plant is unhealthy or nearing the end of its harvestable life but does not define over maturity. Wilting leaves can be a sign of stress or dehydration rather than a direct indication of over maturity. Height exceeding 10 inches does not directly lead to the classification of being over mature, as different varieties of broccoli may have varied optimal heights. Hence, the correct identification of over maturity hinges on the observation of flowers opening.