Is there a way to remove level requirement to Oblivion's quests?

Solution 1:

You can make your own mini-mod for this. Since this sounds more like a question for GameDev, where we develop stuff in preference of using other people's tools ... let's explain how to go about it the "proper" way first:

1. If not already done so, install The Elder Scrolls Construction Set (version 1.2 is fine; you need the older 1.0 only for few specialised tasks which are broken in the latest version). Optionally, install the Oblivion Script Extender and the Construction Set Extender for significantly easier modding in general.
2. In the TES CS, load the main oblivion.esm by going to the menu item File -> Data, marking the tick to the left side of oblivion.esm, and clicking OK. The loading will take a while.
3. Open the list of quests by picking the menu item Character -> Quests...
4. The quest data window appears, with all the existing quests in the game (even those who aren't "real" quests, or are left-overs from the development) listed.
5. The next step depends on the quest.
   • Some have the level requirements listed right there, in the "quest conditions" part. In such a case, mark the offending line (it has a GetLevel check) with the mouse and hit the [DEL] key on your keyboard to remove it.
   • Other quests have the level check in the topics which start the quest. You'll have to work through the Topics tab and remove such conditions.
   • Some quests have the level condition (again, using player.getLevel) in the quests scripts. Click on the [...] button next to the script name to edit those.
   • Finally, both topic and quest stage result scripts can be used for such checks, but I don't believe any vanilla Oblivion quest does so.

For the lazy and in a hurry, there is a mod which does it for you: No Daedric Quests Level Locks.

(Version 1.2.0416)

Solution 2:

You could use Console Mode. There isn't a way to disable level control, but you could try this:

enable the console, by setting bAllowConsole = 1 in the oblivion.ini
enter the console (tilde key)
sq (shows all game quests with ID, find your quest ID)
setstage <questID> 10

10 is the enter value for every quest. Beware to save before EVERY operation, using console can often lead to bugs and inconsistent states.

Everything about Oblivion Console: http://www.uesp.net/wiki/Oblivion:Console