While I would doubt that people actually lived that long, let me help you out on some stuff here.
1. People in Genesis supposedly lived a very long time and if you believe that time was measured in years it seems likely the sexual maturity of people was at a much later time than people today.
2. From Adam onward, with a few outliers, people died earlier in life than their parents. The most notable jumps are Methuselah (an outlier) to his son Lamech (969 to 777). But then Noah, Lamech's son, was also an outlier 950.
3. Genesis 6:3 explicitly states that God will number the days of man to 120 years. Noah, lived before and after this statement to the age previously stated. However, Shem, Noah's son, lived to be 600. After this time his next three descendants lived into their 400s. Then Peleg is where you really start to see change, 209 when he died, and his two descendants lived similar lifespans. Nahor, however, is the first one that the 120 rule applies to, lived 119 years, dying 81 years younger than his father.
If I were a science fiction writer I would say that this is evidence that God was messing with the genetic code of his test subjects. However, this to me is evidence that the god of the Bible is not really as all powerful and wise as some would make out. If you can actually live for 900 years, you would probably take better care of things and do long term planning.
3. Scientists do and don't know why we age. Our cells will, in the course of a lifetime, make many copies. Over time errors will occur and eventually occur with increasing frequency. The result is aging. What scientists don't know is why those errors occur.
4. There is a way to live double your lifespan but the process involves eating half as much as you do, nearly starving yourself.
5. If you say that science is playing catch up to the Bible you may also want to consider Buddhist though, which science is also confirming in some cases. It was also on the part of Medieval churches that scientific thought was banned and declared heresy for several centuries. During which time Europe suffered great setbacks and road blocks to advancing the quality of life and improving their medicine. Operations like brain surgery (albeit mild forms) were preformed many centuries ago (I believe in Greek, Roman, Arabic, and Oriental cultures) but the sophistication didn't even start to develop until at least the 1800s? Why is that? Because people thought prayer and no action would save them.