Most, but not all, panthara require a trick to tame. Farm up some Fresh Talbuk Meat which is drops rarely from talbuks on Argus; approach your target; throw a Freezing Trap; Feign Death to lose aggro (this is essential for the meat to work); throw the meat directly on top of the panthara; tame quickly! Panthara that do not require this trick are Naroua, Sabuul, and the Shadow Stalkers in The Seat of the Triumvirate dungeon.
Level scaling: Most NPCs will scale with the Hunter's level, within the constraints of their level range. Hunters can tame regular NPCs up to 2 levels higher than them, but can only tame elite NPCs of the hunter's level or below.