Requirements
At what level you can be reborn depends on what class you are:

Archer: Level 120
Fire Taoist: Level 120
Trojan: Level 120
Warrior: Level 120
Water Taoist: Level 110
Ninja: Level 120
Monk/Saint: Level 120

For most classes, the required level to be reborn is 120. However, Water Taoist can have first rebirth when they reach level 110, because they have greater spiritual awareness than the others and they always heal and cure instead of destroying.

What if I'm level 130?
You can be reborn at level 120 or above. And if you are reborn at level 129+, you will get more bonus attributes (55 at most) after rebirth. Characters that were reborn above level 129 have a kind of epiphany. For example, a player was reborn at level 135 with 30% EXP, he will be able to leap to level 135 with 30% EXP as soon as he reaches level 130 again after rebirth.