Enemy health, stamina, and magicka is always scaled according to player level. Additionally, enemy stats, resistances, abilities, greater and lesser powers, possible equipment, and spells will level accordingly with the player.
The level at which new items, new enemies, leveled chests, enemy equipment, leveled quest reward items, and leveled drops cease to increase is 25. At this point, you will have access to the best of all items. Please note that some items are glitched, so some levels of items will not have the proper effects that they claim to have.
For any and all other questions, please read the unofficial (though very thorough) Elder Scrolls wiki [http://www.uesp.net/]. It has basically anything you've ever wanted to know, and then some.
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