How do you know that jesus died at age 33?

Ok, so the site http://en.wikipedia.org/wiki/Judas_Iscariot says that judas, the one that had jesus killed, killed himself between 29-33 A.D. So why doesn't it just say that he killed himself in 33A.D. because he killed himself after he helped jesus get killed? And how do you know that jesus was killed at age 33?
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