[url=https://www.wizard101.com/]

Sure you'll love it,

For serious answers, you've got Magicka (#m-m-mainstream suggestion!) and this beta game Lichdom which I haven't played but advertises itself as magic focused. Really I don't know what your "idea of being a wizard" is and those are the two most magic centric RPGs I can think of. It's sadly not as big of a thing as it should be.