How did the people in the Bible live to be 800+ years old?

I'm not trying to refute the Bible or anything, it's just been something I've always wondered. The only explanation I've heard is that it was because of the canopy of water that was above the earth before the great flood, which protected against the sun's radiation better than the ozone does today. Did people still look like children at age 30? Still look in your prime at age 200? Or did you grow into an adult at the same rate as today and then it slowed down...? So confusing. Or did you grow into an old man/woman at the same rate as today, then you just stayed old for 700 years...?