There are no level requirements to any of the specific quests.
The farmer quests are split into 3 sections with 32 quests in each section, the first section is immediately available from level 1
When you are level 80 you can access the hero quest, completing that will give you access to hero village and enable the other 2 sections of the farmer quests
If you are asking "at what level will I reasonably be able to complete each quest" then that depends on your class, how good your kit is, what books/skills/spells you have, and your actual skill as a player. Part of the fun is trying them out for yourself, they are vaguely in order of difficulty but not quite. Try to do them in order and if you come to one that's too difficult just skip it until later and try the next one