Most children can speak five-six coherent sentences at

The correct option is three years.

Language development in children progresses through predictable, age-appropriate milestones as they grow:

• One Year: At this stage, a child's speech is usually limited to single words (such as "mama", "dada", or "bye-bye") and imitating sounds.
• Two Years: Children begin to join two or more words together to make simple phrases, such as "more milk" or "doggy run".
• Three Years: This is a period of rapid language development. By three years of age, a child's vocabulary typically grows to about 500 to 1000 words. Most children can speak in coherent sentences containing four to six words, ask questions, tell simple stories, and carry on a basic conversation.
• Five Years: Children at this age can speak clearly in complex, grammatically correct sentences and tell longer stories.

Thus, the milestone of being able to speak five-to-six word coherent sentences is typically achieved at three years of age.