I got some lvl 80 characters that was created before the achievement system were implented.
And now when i log in, those characters don’t got any achievments although i have made alot of quests and other stuff that grant points.
Is there any way to claim these points afterwards?
Go to the Chronicler in any main city and let him update it (quests, PvP kills and levels, character levels and milestones, factions and so on). Killed enemies wont be update, you will need to hunt them again. For pets you just summon them once and they will be updated in your achievements window, same goes for mounts.
The Chroniclers in Khemi is near the guy that takes you to Khitai, the Chronicler in Tarantia is near the barracks where you can change items for renown (and the PvP zone travel guy) and in Conarch he is standing near the big hut if you walk over the bridge near the three traders and the tavern. They are marked on the map as a green dot.
Thx alot! 
You might need to ask him to update the quest section a couple of times. I seem to remember needing to do that until everything it should have captured was updated.
Keep in mind that it does not take into account any raids or dungeons (or even if you did purist dungeons as you leveled up years ago) that you might have done before the achievement point system was in place. It will however update your quests, factions, 80s, and pvp levels (and maybe your kill count), but make sure to log into each toon to take to the chronicler npc.