We know that this threshold exists, because we don't get age-related diseases until we're in middle age, even though the damage has been accumulating since before we were born.
我们知道这个门槛程度的存在， 因为我们只有当我们在中年时才会得到与年龄有关的疾病， 即使损害已经从我们诞生时就开始累积了。