PVP is only allowed post level 45, and yes you can be engaged at any time outside of safe zones but there is a significant "karma" penalty incurred when doing a random PK. When a player gets below a certain karma threshold they are actually banned from all cities and are considered KOS for everyone, among other disadvantages. Even in safe zones. Meaning no bank, merchants, marketplace, stables, or repair services. All things you NEED at least once every hour or two. You can only regain karma by grinding mobs, but the rate is quite slow so recovering from the PK penalty is nothing to sneeze at. AFAIK it takes an hour or two grinding AT LEVEL mobs to recover from ONE PK.
That being said, there is a bit of an oversight/bug right now where someone will initiate a PK but if they start to lose it they will flag down. There is currently no cooldown for the PVP flag and it is being abused, but I don't think it will last long. Daum and PA really frown on this type of behavior, and have done their best to discourage it all the while promoting GvG warfare which is where the majority of PvP happens. Guild wars start roughly every 5-10 minutes and can end in 20 minutes to 6 hours (Longest one I've seen so far). The way guild wars work is all the members of the guilds are KOS for all the players of the opposing guild and there is no karma penalty for killing them, nor do they have to flag up to kill. Guild wars also involve ALL players of the guilds including the ones below the normal PVP threshold.
In short, PVP is a bit of shitshow right now due to there being no cooldown on the PVP flag but once that gets addressed I'll bet it will become more like what the KR version looks like with very little random PK (mainly contained within the high level grinding spots) and massive guild wars that span weeks at a time. The Valencian Desert (the iconic Black Desert, not in our version yet. Won't be for months yet.) is a bit different but that won't be in our version for a while yet.
Also, the penalty for dying during a PK is not bad. A normal PVE death causes you to lose XP and there is a chance for your equipment gems to break, however in PVP you only have a chance of your gems breaking and you do not actually lose XP. Unless you're a criminal (someone with negative karma), if you're a criminal you suffer the biggest penalties with loss of Gems, dropping gear, destruction of gear (if severely negative Karma), and randomized respawn location (within region of death).