Short Description
This mod seeks to mirror the level/skill restrictions found in some RPGs and MMOs regarding usable equipment.
Weapons, armor and magic will now have skill requirements to be usable.  Also, weapons can break if used with not enough skill.
The player can choose two modes of play:
1) Penalties / de-buffs for wielding weapons and wearing armor above their level
2) Or simply having weapon or armor piece automatically unequipped if the players skill level is too low

NOTE: IF YOU DO NOT CARE FOR THE BREAKAGE ASPECT, YOU CAN TURN IT OFF IN MCM EMNU OR USE OTHER VERSION OF MOD AT: https://www.nexusmods.com/skyrimspecialedition/mods/22830

Long Description
When equipping weapons and armor, this mod will check to see if the player
character meets skill requirements. As of v2.0, weapons are dealt with
in the style of Dark Souls: the player can still attempt to swing the
weapon, but will deal less damage, suffer heavy stamina damage, and be
staggered/stunned temporarily. As of v2.5, armors are also no longer
simply unequipped. Higher-level armor can still used, but at the cost of
decreased effectiveness and, in the case of Heavy Armor, increased
encumbrance. With the MCM menu, the skill requirements for each material
type can be modified, and the mod can be made to affect or not affect
Heavy Armor, Light Armor, Archery Weapons, One-Handed Weapons,
Two-Handed Weapons, equipment used to block, and Magic. v2.6 adds
support for shields and magic spells. Higher-level shields (and weapons
for which the player fails the Block skill test) will cause staggering
to the wielder when they block or bash. Higher-level magic can be used
at the cost of lower effectiveness (Destruction and Restoration), lower
duration (Conjuration and Illusion), and higher cost (Alteration).

To explain the mod with an example, assume that the player has set the
skill requirement for Iron equipment to 50; for the purposes of the
example, this player has a One-Handed skill of 60, a Two-Handed skill of
40, a Block skill of 45, and a Heavy Armor skill of 35. The player may
equip an Iron Sword without issue. As of v2.0, attempting to swing an
Iron Warhammer will have the player deal significantly less damage and
suffer staggering and stamina damage. In Dark Souls, the concept is that
you lack the strength/dexterity to effectively wield the weapon, which
results in your epic-ly failed swings. Bows which the player cannot use
effectively will not cause the stamina damage and staggering, but will
also deal significantly reduced damage. As of v2.5, the player's attempt
to equip an Iron Helmet will result in the helmet being 15% less
effective and increasing encumbrance. Similarly, higher-level Light
Armor pieces are 30% less effective, but don't affect encumbrance. As of
v2.6, the player's attempt to block or bash with the Iron weapons will
cause the player to be staggered.

By default, the mod affects Heavy Armor, Light Armor, Archery Weapons, One-Handed Weapons,
Two-Handed Weapons, equipment used to block, and Magic, and the level
requirements are as follows:
Draugr, Hide (and Forsworn), Imperial, Iron, Leather (and Thieves Guild), Stormcloak, Wood - 0
Bonemold, Steel (and Dawnguard), Studded - 20
Chitin, Elven, Falmer, Glass - 30
Aetherium, Dwarven, Nordic, Orcish - 40
Ebony, Stalhrim - 50
Daedric, Dragon - 60
Novice - 0
Apprentice - 20
Adept - 40
Expert - 60
Master - 80

v2.6.5 adds a new MCM option that incorporates a minor feature. Now, weapon swings when the player has 0 stamina will cause a staggering
effect, if the feature is enabled.

Requirements
Latest Official Skyrim Patch (v1.9.32.0.8)
Dawnguard and Dragonborn DLCs (optional, RE: Files)
SKSE
SkyUI (Highly recommended to allow customization and safer uninstallation)

Installation
Extract and merge contents with Data folder.
Can be placed anywhere in load order because it does not edit any Vanilla
objects, and is thus fully compatible with all other mods.

Updating
Unequip all equipment and save. Overwrite the files.

Uninstallation
Unequip all equipment, and use the Uninstall option in the MCM (if possible,
otherwise a clean uninstall is not really possible).
Save, quit, uninstall the mod, reload, and save again.

FAQ (or, at least, good concept-related questions)
Isn't this mod useless since Skyrim levels with the player, so they won't see
higher-level equipment until they are a higher level?
A lot of people use mods that delevel the world, like SkyRe and Requiem, so they
can encounter higher-level equipment at low levels. Even without these
mods, consider a high-level character specializing in Two-Handed
weapons. They will be able to pick up some high-level One-Handed
weapons, but probably would not be able to use them due to this mod. In a
sense, this mod discourages multi-classing and encourages
specialization. Additionally, even the the Vanilla game, many unique
items that would qualify as higher-level items are available early in
the game, so this mod discourages their premature use.

Isn't a sword just a sword? Why should you wield one more effectively than another?
Consider that high-level swords are heavier. That means that you need more
experience to deal with the new weight properly, which explains why a
lower-level player will wield a higher-level sword less effectively.

Isn't this sort of system better suited to games based on skill investment rather than skill progression?
I agree, but I feel that it still works quite well with Skyrim's system
despite this. You could always use a mod like Skyrim Experience Mod if
you prefer skill investment.

Does this affect custom equipment from other mods?
If the mod author added Keywords properly, it should affect that equipment or magic.

Does this mod conflict with any mods?
This mod was designed for maximum compatibility. I didn't edit any existing
perks/weapons/armor/quests/etc. The only conflicts might be stylistic.
For example, if you use a mod that gives you stamina as you swing a
weapon (which doesn't make any sense), it will cancel out the stamina
damage that my mod causes.

Thanks
R0R0N0 for the mod idea.
CGi for help with the MCM localization.
ww13 for the German translation of the MCM.
monbabii for help with the mod concept.
Chesko for a script that prevents the unequip-enchantment-charge bug.