I mean, as a mage, you’re depending a little on how you’re specc’ed, (but you’re probably specc’ed to do the most damage with Frost Bolt), you aren’t super gear dependent, and will do better dmg than some other classes, even in whatever gear you happen to be in.
I wouldn’t worry too much about it, but have a look at some pre-BiS lists, like https://classic.wowhead.com/guides/wow-classic-mage-dps-pre-raid-best-in-slot-gear
It’s arguably better if you can get a sense for yourself as to the stats that are helpful for you, rather than just the gear, but it’s also easy to just follow a shopping list, so you do you.