For most people fear of death does seem to decrease with age.
As a person ages the fear of death is usually less and less and the person usually starts accepting that they will die eventually.
Me I used to have a fear of death as a teenager but after I turned 25 my fear of death lessened and now that I'm nearing 35 years old I really have no more fear of death.
I have already accepted that death is gonna happen and since we cannot stop out death from happening or cannot stop the death of anyone from happening then there's nothing else we can do but learn to accept it.
Basically death is just like when you go to sleep at night.
Except when you die you sleep permanently and no longer wake up.
I have no belief in god or Jesus or the afterlife but I accept that I will no longer be alive one day.