I had the same issue with level 10 quests. I was level 8, it let me take the quests (presumably because my main class is 29 even though I was my level 8 conj at the time).

I accepted the quest as level 8 conj, vanquished the mobs as a level 8 conj but couldn't turn it in as a level 8 conj because it said i need to be level 10. I was like seriously?!

A few examples would be the missing lunch quest over at moraby drydocks, the bridge full quest near there, etc. I had 6 quests completed that I couldn't turn in and it was to the point where I'd have to grind to get to level 10 just to turn them in because i used my leve allowances on my maelstrom seal leves. Needless to say I was quite annoyed.