1. Is there a class that requires a more active pro-active playstyle like Warden in Lotro or Monk in WoW in later levels. So far I've found the tank classes in the early lvs to be very very basic rotations, very simple rotations bore me quickly.
Right now, Guardians and Shadows both fit the bill for active play but in different senses. Guardians have the most complex prioritization and is the least forgiving of mistakes. Shadows have a less complex explicit rotation, but it is more random and has a greater impact on total performance.
When RotHC is released, this is going to change somewhat. Guardians are getting simplified somewhat and are getting an extra CD and Shadows are largely staying the same. VGs are also getting made a bit more complex with the addition of the Shoulder Cannon and self healing derived from it and Adrenaline Rush, not to mention the tweaks to Smoke Grenade. At that point, all of the tanks are going to become pretty proactive.
2. When do tanks start getting gear to increase shield % and absorb rating. My highest lv 'tank' so far is only in her 20s but I'm still at the 5% chance 20% absorb.
You'll start seeing gear with defense and/or absorb on it in your early 20s, but not in appreciable amounts. You don't start seeing Shield at all and Defense/Absorb in appreciable quantities until your 30s.
3. Follow up to #2 Are these increases stat based or just better shield generators?
All shield generators have the same 5% shield chance and 20% absorb chance baseline. Until you get into your 30-40s, a vast majority of your tank stats (Defense, Shield, Absorb) are going to be derived from talents and class abilities (all tank stances provide 15% shield chance; Shadows get Kinetic Ward, Shadowsight, and DBSD before the early 20s; Guardians get Blade Barricade and Guard Stance; VGs get Rebraced Armor, Shield Cycler, Ceramic Plating, and Smoke Grenade).