The answer of the question lies in the word ZERO. According to vedas, the most prominent answer to define Param Atman is Shunya ( Zero ). Another thing to help is Bhagwat Gita, every action ( Karma ) has a response and that too equal in nature, meaning if your did good you'll get good in return not only in the same form but also in the same amount.
Moving forward if you haven't done anything, you have actually neither gained good or bad, you are in Zero Karmic State, or Zero itself, partially the Param Atman.
But There cannot be 2 Param Atmans, their only one exists and will always exist. In such case the 2 combine or merge to become one, which in results acts as liberation of the soul.
Bottom Note : No Karmas then No results, hence Liberation. And the soul's PARAM goal is to attain Shunya or Param Atman. And if you did Karmas you are destined to get results from it, whatever manner or intention you have applied to it. But if you do in manner of not doing its equal to Shunya ( or No Karma at all), this is considered under Akarmic States of Soul.
Will a man attain liberation the moment his karma is nullified? YES, whatever age he is in, student, mature or sadhu. Once the Atman is liberated it vanishes, you may only find body lying under, many would consider it death, and that could also be. There have been incidents when the world has lost people who were neither old, nor had any type of body deficiencies but died, those can be liberation but not death.