to get up tp 66 agility fast i did the wildy course at lv 52 and u get 500 exp per lap which it takes me like a min per lap. After 75 you can train on Ape troll as you wont fail. After 85 you can do extended agility training like gnome.
For starters as lvl 1 agility, you can use Gnome Agility Course located near the Gnome Stronghold. You can go to Wilderness Agility Course at level 50 and it's a good way of getting fast agility, but...