C180 Each Had Their Own Strengths.
In fact, it was not impossible for him to 'forbid' others from aging.
The problem was that Zhang Ping did not understand genetic engineering, nor could he directly observe his own genes.
Moreover, even if he knew about this, he would not be able to order others to do so, because they did not understand it.
Simply put, if he wanted to make the target who swallowed the Contract Gem not grow old