Life election for anything in a "democratic" country really makes no sense.
The whole point of America is that no one regime has omnipotent rule and that is exactly what has been constituted. If a judge is 80 years old how can he or she adapt to the changing times with any accuracy?
This isn't to say every old person can't change, but it is alot harder when you have been doing the same thing for 40 years.
Also I don't think younger people should be judges, there should be an over 30 age limit, but there should be re-election so that judges cannot get too comfortable in their positions and forget about what the people really need.