Gravity is 9.8 meters per second. It's a 9.2 mile fall. so just divide the two and you get 0.9388 seconds.
As they get older, they become less mobile.
Yes this is true as in cold conditions our body doesn't feel the urge of water therefore we may become dehydrated not even knowing about it and of course in hot coditions we sweat therefore we loose water.
Hope this helps :).