I cannot for the life of me find anything on guardian past level 30 and just wondering.
Assuming you meant to say Gladiator (although I think Guardian would be a cooler name), there are PLENTY of skills above level 30 for Gladiators, check out this link
for those skills. Paladin is what is called a "Job", it specializes you and grants you access to certain abilities obtained via quest every 5 levels, which are extremely powerful. Things like increases you auto attack damage by 50%, increasing your block rating, taking all of the damage for a fellow group member for a short period of time, etc. However, have a Paladin soul equipped limits the Cross-Class abilities you can use. You can no longer use those nifty Pugilist skills like featherfoot and the self heal - instead, you can only use Marauder, Gladiator, Paladin, and Conjurer skills. Most people agree that the benefits gained by taking on a job far outweigh the benefits lost.
You Paladin job soul will basically just grant you those abilities, but the Gladiator and Paladin experiences are linked together. If you are a level 45 Paladin, you are also a level 45 Gladiator, if you take your soul off. They work in conjunction, just like a White Mage job soul works with a conjurer, or a Bard job soul works with an Archer.
You can always take off your Pally soul, level the appropriate classes, then take a new job in addition to Paladin, you should can't equip two at once, and you must be armor speced for the correct class to become that class's job. That last part seemed confusing as I was writing it - but I'm sure you understand.