Full answer (lack of training)
This age is the time of early childhood and the child is not old enough for the development of the personality of a leader. Then how did his personality develop?The answer is that several of his forefathers also assumed the Imamate at an early age. Imam Muhammad ibn Ali al-Jawad assumed it when he was only eight years old and Imam Ali ibn Muhammad al-Hadi when he was only nine. The phenomenon of the early Imamate reached its zenith in the case of the Imam Mahdi. We call it a phenomenon, because it assumed a tangible and practical form as in the case of Imam Mahdi's forefathers. It was felt and experienced by the Muslims coming into contact with the Imam concerned. Experience of the people being the best proof of a phenomenon, we cannot be asked to give a more tangible or a more convincing proof of it.
The following points will elucidate what we mean:
(i) The Imamate of an Imam belonging to the Holy House was not a centre of hereditary power and influence, nor did it have the backing of any ruling regime, as was the case with the Imamate of the Fatimid caliphs and the caliphate of the Abbasid caliphs. The extensive popular support and allegiance which the Imams enjoyed was due only to their spiritual influence and the conviction of their followers that they alone deserved the leadership of Islam on spiritual and intellectual grounds.
(ii) The popular bases supporting the Imamate had existed since the early days of the Islamic era. They expanded further during the time of the Imam Baqir and Imam Sadiq. The school set up by them assumed the form of an extensive intellectual movement which included among its ranks hundreds of legists, scholastic theologians, exegetes and others learned in various fields of Islamic scholarship and the humanities known at that time. Hasan ibn Ali Washsha, when visiting the Masjid of Kufah, found there 900 scholars all repeating the traditions narrated to them by Imam Ja'far ibn Muhammad al-Sadiq.
(iii) The qualifications which an Imam possessed, as believed in by this school and the popular bases represented by it, were very high. The Imam was judged by the standard of these qualifications to find out whether he was really fit to be an Imam. They believed that the Imam must be the most learned and wise man of his time.
(iv) The school and the popular bases had to make great sacrifices for the sake of their belief in the Imamate which the contemporary governments regarded as a hostile line, at least from the ideological angle. This attitude led the then authorities to the persecution of the followers of the Imams. Many people were killed. Many others were thrown into dungeons. Hundreds died while in detention. Their belief in the Imamate of the Prophet's House used to cost them dear. The only attraction was their conviction of gaining the favour of Allah.
(v) The Imams, whose Imamate these popular bases acknowledged, were not living like the kings in high towers isolated from their followers. They never segregated themselves, except when imprisoned, exiled or forcibly kept aloof by the ruling juntas. This we know for certain on the authority of a large number of reporters who have narrated the sayings 'and deeds of each of the first eleven Imams. Similarly, we have a record of the correspondence exchanged between the Imams and their contemporaries.
The Imams used to make journeys to various places and appointed their deputies in different parts of the Muslim world. Their supporters also, while visiting the holy places during Hajj, made it a point to call on them at Madina. All this meant continuous contact between the Imams and their followers scattered all over the Muslim world.
(vi) The contemporary caliphs always regarded the Imams and their spiritual leadership as a threat to themselves and their dynasty. For this reason, they did all they could to disrupt this leadership and in pursuance of their nefarious ends, they resorted to many mean and arbitrary actions. Occasionally their behaviour was too harsh and despotic. The Imams themselves were continuously chased and kept in detention. Such actions were painful and disgusting to all the Muslims, especially to the supporters of the Imams.
These six points comprise historical facts. If we take them into consideration, we can easily come to the conclusion that the early Imamate was a real fact and not a fiction. It is certain that an Imam who appeared on the scene at a very early age, who proclaimed himself to be the spiritual and intellectual leader of the Muslims and who was acknowledged to be so by a vast cross-section of the people must have had great knowledge, competence and mastery over all branches of theology. Otherwise, the popular bases could not be convinced of his Imamate.
We have already said that these bases had continuous contact with the Imams and were in a position to judge their personalities. It is not conceivable that so many people should have accepted a boy to be their Imam and should have made sacrifices for his sake without ascertaining his real worth and assessing his competence. Even if it is presumed that the people made no immediate efforts to ascertain the position, still the truth could not remain unknown for years in spite of the continuous contact between the child Imam and the people. Had he been childish in his knowledge and thinking, he would certainly have been exposed.
Even if it is supposed that the popular bases of the Imamate could not discover the truth, it was easy for the government of the day to expose the child, if he had been really childish in his thinking and cultural attainments like all other children. It certainly would have been in the interest of the government of the day to bring him before his supporters and others to prove that he was not fit to be an Imam and a spiritual and intellectual leader.
It might have been difficult to prove the incompetence of a man of 40 to 50, but it would have been quite easy to prove the incompetence of an ordinary child, howsoever intelligent he might have been. Evidently, this would have been much simpler and easier than the complex and risky policy of suppression adopted by those in power at that time.
The only explanation for why the government kept quiet and did not play this card is that it had realized that the early Imamate was a real phenomenon and not a concoction.
The fact is that the government did attempt to play that card but did not succeed. History tells us of such attempts and their failures, but it does not report any occasion on which the child Imam vacillated or showed signs of such embarrassment as could shake the confidence of the people believing in his early Imamate.
That is what we meant when we said that the early Imamate was really a phenomenon and not a mere presumption. This phenomenon has deep roots, for there exist parallel cases throughout the history of the heavenly mission and Divine leadership.
We cite just one instance : We commanded John; Zachariah's son, to follow the guidance of the Lord with due steadfastness. To John We gave knowledge and wisdom during his childhood', (Surah Maryam, 19.12)
After it has been proved that the early Imamate had been a real phenomenon already existing in the life of the people of the Prophet's House, no exception can be taken to the Imamate of the Mahdi and his succession to his father while he was still a child.