Clark and Lex were friends at the beginning in the comics. But as the story progressed, Lex's character changed, and they became enemies. This transformation was driven by Lex's mistrust and his own ambitions.
Lex Luthor's age isn't fixed in the comics. It can change based on the creative direction of the writers and the era of the story. Generally, he's portrayed as an adult in his prime, often in his late 30s to 50s.
Lana Lang did not marry Lex in the comics. The comic plots didn't lead to such a union. Their characters had separate developments and romantic involvements.
Well, Lex Luthor's death varies depending on the comic storyline. Sometimes it's due to his own schemes backfiring, other times it's at the hands of a powerful foe.