I don’t think it’s always intentional. It’s very common for people under 25 to feel immortal, especially mid teens. It’s probably one of the reasons why militaries like to grab people from late teens/early 20s. Takes advantage of that common trait. after all, if your army is full of people who feel invincible, you can convince them to do things that they might not do if they had a regular fear of death.
There’s always a few who die from recklessness. People who can’t control their tempers. Get deep into drugs/alcohol. People who eat UNBELIEVABLY poorly. People with short family lifespans. And of course random accidents.
So, yeah, I agree. It’s nice that none of them died early.