Verse 6. And Noah was six hundred years old.
"It is not without reason that he again mentions the age of Noah. 
---For old age has this among other evils, that it renders men more indolent and morose; whence the faith of Noah was the more conspicuous, because it did not fail him in that advanced period of life. And as it was a great excellence, not to languish through successive centuries, so big promptitude deserves no little commendation; because, being commanded to enter the ark, he immediately obeyed.
When Moses shortly afterwards subjoins, that he had entered on account of the waters of the deluge,
---the words ought not to be expounded, as if he were compelled, by the rushing of the waters, to flee into the ark; but that he, being moved with fear by the word, perceived by faith the approach of that deluge which all others ridiculed.
Wherefore, his faith is again commended in this place, because, indeed, he raised his eyes above heaven and earth."
Calvin