This is my opinion,I believe in the vapor canopy theory,Genisis 2:5-6 5 before any plant of the field was in the earth and before any herb of the field had grown. For the Lord God had not caused it to rain on the earth, and there was no man to till the ground; 6 but a mist went up from the earth and watered the whole face of the ground. The mist could have blocked the sun's radiation keeping everything from being aged by the sun and since reptiles and certain mammals continue to grow until they die,maybe after the flood the mist vapor was gone allowing the sun's harmful rays to age everything and I don't think they were taking giant full grown creatures on the ark but more than likely babies without blemish,I don't know just a thought,I'm sure some of you have heard this theory before