My youngest daughter actually started talking very early. When she was 7 months old my DH was headed to a meeting and stopped before going out the door, saying "Bye bye, Melissa". She looked up from her chair, raised her hand, and said "bye". She knew exactly what she was doing, but we just stared at each other for the longest time.
So, by the time she was about 18 months old she had a large repertoire of words. One night she was playing with a large box I had given her. She got throw pillows and a blanket, arranged them in the box, then climbed inside. The sat down, leaned back with her arms raised and her hands behind her head, and said "Now I'm comfortable". I think that was the first time she had made a complete sentence. It just floored me that one so little could understand the meaning of comfortable, plus be able to say it.
And today, at 29, she has proved herself to be a very intelligent and articulate young woman.