Is a conditional bequest appointing an executor upon the fulfillment of a condition valid?

Primary text

If a testator states, 'I appoint you as my executor, and when my son becomes mature, he shall be my executor,' this is valid. The son becomes the executor upon maturity. This principle applies equally if the condition is that the son ceases his wickedness (fisq), returns from absence, recovers from illness, dedicates himself to knowledge, reconciles with his mother, or becomes of sound judgment (rushd). The bequest to the alternate person is valid, and that person becomes the executor upon the condition being met.