To get more HP than that legitamately as a L22 mage (and this is what I do with my Kensai to L21, then dual to mage allows advancement to L22...)...
9*10 = 90 (first 9 levels of advancement of fighters with max HP)
9*6 = 54 (constitution 22 (wont see the benefits of this until the fear tear))
12*3 = 36 (12 levels of 3HP per level, between levels 10 and 21)
10 (deck of many things, ToB)
12/24 (depending on familiar, 12hp. ToB, 24hp)
15 Greed tear
Total:
205 + familiar 12/24 = 217/229 ToB. But we can do better than that
Pale green Ioun stone, +10% hp so...
205 + 10% = 225.5 (rounded up/down? I don't know). +24 ToB familiar gives an impressive 249.5HP permenanently in effect.
Dual wield Katanas. Grand Mastery. Stoneskin, Improved Haste, Tensers Transformation = Much scariness.
Enjoy kiddies