At the present time, there isn’t a way to get or set the level of a Villager.

• VillagerData: Information about the villager’s type, profession, and level.
  level: The current xp level of this villager's profession. Influences the trading options generated by the villager. If it is greater than their profession's maximum level, no new offers are generated. Increments when the villager fills his trading xp bar. Also used for badge rendering.

Ideally, there should be getLevel() and setLevel() methods for Villagers.

Thanks!