Other than the fact that warlocks get minions, they both are casters that use magic for dps. I have made a mage AND a warlock but both are low levels and want to know what's the main difference? Specifically for dps/pve?

Depending on spec, warlocks either to most of their damage via DoTs (damage over time spells) or fire damage. The mechanics are different as you use soul shard, and mana is much less of an issue due to lifetapping.

Warlocks are generally beefier than mages, much more difficult to kill. This makes PVPing with a warlock easier.

Warlocks have a lot of versatility. I've been in raids where we use warlocks as tanks on certain encounters where the mob can't be in melee range but needs a tank. (Mirmidon's head for example)

But as mages are able to generally do better burst damage, this can make them much more deadly in PVP. However they are much squishier, hence their spells to get out of trouble (blink, iceblock etc)

In raids and dungeons, depending on the current patch and balance, mages tend to top damage meters. I have played both characters to 80, and the styles are quite different. However as I tend to play quickly, as I am a fidgety gamer, I much preferred playing a mage.

Well, I don't really do Warlocks that well, because mine is in the 40s, but I do have several 85 toons and I can tell you that from what I know, Warlocks are more of DoT (Damage over Time) and they normally have minions. They're like the dark magic that give curses and poison you and do all these necromantic spells on you. They literally raise hell on people. (Look up the skill Hellfire in the Warlock category and you'll catch my pun) <-- Hah.

Mages are more straight forward, not dark, but they use a specific magical attribute (Arcane, Fire, or Frost) and deal damage with that.
Arcane is well, straight arcane and intellectual damage.
Fire has DoTs and does lots of decent damage (sometimes good for pvp if skilled in fire mage)
Frost is more for PvP alone and good for slowing people down.

Personally, I like them both, but my mage is a lot higher of a level, only because I was required to get my mage up for my guild.

I hope this helps!(: