Final answer:
The facet of cognitive development that continuously improves throughout life is language development. While children quickly master their native language due to a biological predisposition, the proficiency to learn new languages is highest during the early years, becoming more challenging as one grows older.
Step-by-step explanation:
The facet of cognitive development that improves throughout life, particularly in terms of language acquisition and proficiency, is known as language development. Children are biologically predisposed to language learning, and they begin to develop these skills from a very early age, mastering their native language remarkably quickly. Language acquisition is believed to follow a similar pattern across different cultures, indicating a universal aspect to this process. It's during the early years that children show the greatest proficiency in learning a new language, supporting the concept of a critical period for language acquisition. As they grow older, mastering additional languages becomes more challenging.
Language proficiency continues to evolve and mature throughout life in various capacities. Even as the ease of learning a new language might diminish, the depth and complexity of mastering one's native language or improving multilingual skills can grow. Adults often refine their use of language structures, grammar, and vocabulary, applying these skills in diverse and sophisticated ways. Hence, language development is not static but rather a lifelong process influenced by continuous learning, exposure, and the need for effective communication.