I guess it's weird to me that this list filters for age and then compares 24 year olds to 19 year olds. Seems too broad a range.
It's definitely not easy to compare a player who has been in the league for 4 or 5 seasons to a rookie or 2nd year player.
Most of these players in their 4th or 5th seasons have already seen the vast majority of growth in their games and are what they are save for some refinement. The younger players mostly still have yet to have see the major improvements in their games we hope for.
In other words, you're judging some players based on a theoretical ceiling, while other players you're mostly judging them on what is pretty close to a finished product.
For example, Otto Porter is clearly a currently better player than Jaylen Brown. But Brown clearly has a higher ceiling right now. The question then becomes how likely is it Brown reaches his ceiling, and if he doesn't reach it, where does that leave him. If. Brown reaches 80% of his potential, is that better or worse than where Porter currently is, or may end up with a limit more refinement to his game that comes as a player reaches his prime years.