Tom made a stock and it's simmering the bones and the mirepoix of his stock a second time tom is creating what someone answer you so much

Tom is most likely making a Remouillage. It is French for "re-wetting." It is stock that was made from bones that were already used in a previous stock. It is also known as "Second stock." The bones would be re-simmered and fresh mirepoix added. The result of a Remouillage will not be as clear as the original stock and is a bit weaker. 

The answer would be age 18.