Board Thread:Tapped Out Help/@comment-198.188.130.204-20131108184538/@comment-162.27.9.20-20131112005806

The quests are part of a group or "chain" of quests. Reaching level 24 alone won't necessarily make quests appear - you have to do their prerequisites first. If you don't do everything needed to unlock a quest, you can be level 35 and still not have the quest show up.