From UESPwiki

Enemy Scaling
Creatures do not scale to your level; their stats are fixed.(Morrowind)
Most enemies will be level-dependent, and will be more powerful when you are a higher level. Different and more powerful variations of enemies appear at higher levels.(Oblivion)
Most enemies will be level-dependent, and will be more powerful when you are a higher level. Most enemies have a level range, restricting their leveling to minimum and maximum levels.(Skyrim)