Hi there, i have seen that curently in game there's close to no harm in the toxic behavior about power abusing lower level players, as rewarding as power can be for those who have it, seeing players lvl 40+ going in zergs against players who are bellow 20 is a great no for new players since their agressors don't have any kind of punishment for having that behavior, while they can't do activities that they are supose to do at their curent level, actually is quite the oposite, the agressors earn by repeating this.
I have a few ideas, one of them is adding a level limit to pk, something like 5 levels of distance at max or something like that. I supose that the idea of pvp quests is to have a real incentive to pvp, killing low level people to complete their quests or gain rep doesn't make any sense, is a mechanic that pushes people in to abusing.
Other way that it could work is as a demerit, if you ever kill someone that's bellow the distance of 5 levels from you, you actually loose progress of your quest or loose reputation, since doen't make sense to your rep grown if you are not fighting against someone who can react to what you're doing.
The game itself has its own barriers and having mechanics that allows to older players to push away new ones doesn't seem as a viable strategy gaming wise.
Other way that could work as a less punishing way is that you should not receive death penaltys if you got killed by someone who is 5/10/20/30 levels ahead of you.
Sorry for the spelling mistakes, english is not my mother language and i didn't run a grammar check on the text, but i'm sure that the idea is quite possible to understand.