Naruto would likely be very open and friendly, while Waller would be more guarded and calculating. Naruto might try to befriend Waller right away, but she would be skeptical of his motives and powers. For example, Naruto could offer to help her with a problem using his ninja skills, but Waller would wonder what he wants in return.
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.
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.