So,

I’m looking for advice. My Dark elf Assassin thief is level 51. I’ve finished all the thieves guild and Assassin quests. About half the main quest (I think), and a whole ass load of side quests. I want to start playing a mage, but I think my thief is too far gone down his path to be effective (I haven’t put any points in magic yet). How much more is there to do in the game for my thief? I’m role-playing him as the ultimate badass (leads the thieves and assassins guild), but is starting to feel guilty so he wants to make things right. I guess I could do the civil war. I just cant think of anything else that RPs well.

I want to see the mage guild quests, but I don’t really want to do all the other quests over again. I don’t see how it’s possible to get to level 80 as my skills are starting to advance VERY slowly. Is it worth it to send my thief through the mage quests just to see them, or do I need to start a new character to get the full effect, and powers?

If you just want to see the main mages quest line, you could easily do it with your thief. It is a fairly short questline and you do not need particularly good magic skills to do it.

On the other hand, if you want to roleplay a mage, there is a lot you can do with it in Skyrim, despite the dissapointingly short mages guild main questline. For instance, there are quests associated with obtaining master spells, there are radient quests and such, so roleplaying a mage can be fun.

I can't really see any connections to seeking redemption with the College :I
or any guild in fact, they're all either Neutral or Evil o.o

There is no ingame reason to get to 80 or 81. It's academic as the game has already stopped leveling. You won't get any new quests or loot, other than a few that have some skill level requirement.

If you start a new character, you don't have to do any of the quests you have already done again, other than maybe the MQ. Then you can make a character to fit the role you want this time around. I agree that the Mages College is not a large set of quests, but there are plenty of Magey things to do in the game.

However, if you want to complete and get to 80 and go Mage, then figure out if 29 to 30 Perk Points will allow you build the mage you want. Because, that is all you will have to use.

I would recomend starting a new character as a mage, and building those skill trees from the ground up. I personally have found with Skyrim (on Xbox 360) that I have like it better to focus on only a couple factions and the main quest for each character.. my first character, who I was going to try to do every quest line with, started to bog down once I got up into the upper 50's levels, meaning the game wasn't running well.. I think my save file was starting to just get too big.. Plus, I just like fresh starts sometimes with different characters..

but if you are going to go pure mage... you are going want to spend perks in a few of the skill trees. Destruction is kinda a no brainer, but the Conjuration and Illusion schools are going to be very useful as well... you're going to want to enchant stuff too... so that's a lot of perks to spread around to really get good at the pure mage thing.. you going to want to be getting them quickly with the 1-50 leveling speed.

I think a fun way to do it is to kinda run both the main quest and the college quest side by side, so you are gaining the dragonborn goodies, but also working through the mage stuff.. then once you've completed those two, you'll be a pretty high level mage and can the head off and do all the fun miscelaneous stuff, and really kick butt at it.. But hey, it's your character, you gotta do what you want to do. But i don't think taking a fully matured character at +50 levels and then trying to make it a mage when that has not been your focus all along will be very fun. It'll take too long to build up the skill trees.

Put him on the shelf and re-roll a mage, (or Arcane Archer IMO), and go right to Winterhold at beginning...

yeah, unfortunently, ill have to agree with the other people here that the best thing to do might just be to start a new character. As said before, you just wont level fast enough to really feel like mage while your doing the quests. i usually preplan a the direction my character is going to take and then once i do that, the character is done. ive done each of the faction quest lines, and all have been done with different characters who's sole purpose was to complete their respected guilds.

^{Don't forget too that mages use LOTS of magika. If you haven't been increasing that at level-ups you'll be hurtin' for sure.}

Just go with it using your assassin. Think of it as talent scouting, since there are mages within the Dark Brotherhood. You could also RP it as trying to pick up a few tricks, such as the paralysis spell from Alteration.

I went through the mages guild quests on my hunter character. I RP'd her as stalking some wild game to the north and getting caught in a blizzard. She tried to get a room at the inn, but since the fowl weather had chased away her game, she had nothing to trade, so they kicked her out. Not having any another choice, she stumbled into the Mage's College, cozied up to the guard, and the mages set her up in a room to weather the storm, which lasted several days. Over the course of her time there, she made a few friends within the mages guild, despite them having wildly different outlooks from her. She had the most interest in Tolfdir, since he had many stories about the history of Skyrim which she'd never heard. When the storm passed, she agreed to escort Tolfdir to a site he was researching, along with some other mages, to help repay them for sheltering her in the college. And, from there, everything blew out of proportion and she got svcked into a sequence of events she couldn't control.

The escorting part actually worked just like that, since my game glitched out when Tolfdir was supposed to go to Saarthal and for some reason he got stuck somewhere near Falkreath and wouldn't move. So I had to physically go down there. Once I got there, he started moving towards Saarthal along with Brelyna who had teleported with him, so I just went with it and followed them the whole way there. I would scout ahead of them, kill wild game I saw, pick berries, and help fend off attacks. It was quite entertaining.

If you go more thiefly, you can RP it as your character getting wind of a potentially big score that the mages guild was about to uncover. So, you ingratiate yourselves with them in order to get information and access to whatever valuable treasure they were about to dig up so that you could make off with it. Once you start the quest, it's pretty easy to just imagine yourself getting swept up in the events.

Anywho, you could RP it however you want. Point is, you don't need any real mage skills at all to go through the guild quests.