Answer: 1) What Goldsmith means, is that Death, is something all humans experience. Our mortality makes death inevitable and inescapable. Making it a somewhat, permanent condition.
2) "Like sex. death both fascinates youth and makes their elders reticent" I agree with this statement. Youth, are driven by emotions and feeling, making them more fascinated and intrigued by intercourse. They are knew to this aspect of love and life. Elders, may become less amused, and more silent about the topic. Having known it's personal and not something to be shared openly. They keep it to themselves.
Hope this helps (^_^)