In Gen. 6:8-10 we read that by the time Noah was told to build the ark he already had three sons. According to Gen. 6:18, these three sons were already grown and married by the time God told Noah to build the boat. In Gen. 11:10 we read that two years after the flood Shem was only 100 years old. Noah and his family were in the ark one year and 17 days, so that made Shem 96 years of age when he entered the ark. Thus, if he was a grown man and married before Noah was told to build the ark, and since Shem was only 96 years of age when it was finished, it obviously did not take 120 years to build the ark. The 120 years of Gen. 6:3 refers to Adam, not Noah.

Finis J. Dake, God’s Plan for Man, (Lawrenceville, GA: Dake Publishing, Inc., 1949), 34.
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