Im a lvl 11 nord mage now. Is it too early? will it be better to join later? at around what level?

Thanks

You shouldn't run into any trouble at level 11 barring the final mission. There's a very high level dragon priest boss near the end who I believe is level 50. If you're good at the game, you can probably take him with preparation. If you're new to it, I'd reccomend doing some more leveling. You can safely join now, just don't rush straight to the final quest.

Join as soon as you can for the access to spells and training. You can always do the various quest when you are at a higher level. I enjoy finding books for Urag to get some experience.

I joined very soon after leaving Helgen. You need a decent magicka pool first, but that's about it.

I have a new character who plans on joining the College soon just to get Expert Robes of Destruction early in game....Nirya is kind enough to keep them warm for her and a small fine is all it takes to get the robes and continue studying at the College

You can join up right away, just if I were you I wouldn't rush through the questline. Take your time. Like the above poster said, you can always visit Urag in the Arcaneum and help him out. Arniel Gane is another one you can help. Plus the three mages you join up with all have their own mini quest for you to complete.

It's worth mentioning that some of the items you're rewarded with during the CoW questline are in fact leveled. So waiting til you're a higher level also wouldn't be a bad idea