Lumberjacking is the only skill that goes over 90; a few other skills can get to 90 but 50-90 goes pretty slow. Using magic skills in combat gives XP for that type of magic, so those, evasion, combat mastery, toughness, axe mastery can all get to 90. Regeneration can get to 90 but it's difficult (50+ you only get XP from being at low health AND poisoned or on fire). There's no requirement of any skill over Expert (50) except for lumberjacking.