The Imām, peace be upon Him, is proof (Ḥujjah) of Allah even when He is a juvenile

Muḥammad ibn Yaḥyā, from Ibn ʿĪsā, from Ṣafwān, who said: I said to Imām al-Riḍā, peace be upon Him, : We used to ask you before Allah granted you Abū Jaʿfar, peace be upon Him, and You would say: Allah will grant Me a son. Now Allah has indeed granted Him to You, and our eyes are delighted. May Allah never show us a day without You! But if does happen, then to whom will the matter belong?

He, peace be upon Him, pointed with His hand to Abū Jaʿfar, peace be upon Him, who was standing before Him.

I said, May I be your ransom! This one is only three years old!

He, peace be upon Him, replied: That does not harm him in the least. ʿĪsā, peace be upon Him, was made to stand forth with the divine proof (ḥujjah) when he was only three years old.¹

From Ibn Bazīʿ, who said: I asked him, meaning Imām Abū Jaʿfar, peace be upon Him, about a matter concerning the Imamate, and I said: Can the Imām be younger than seven years old?

He replied: Yes, even younger than five years old.²

Qurʾān 9:103

 ﴾Take from their wealth some alms, with which you make them pure and purify them﴿

al-Imām Abū ʿAbd Allāh, peace be upon Him, said: Whoever claims that the Imām needs what is in the hands of the people is a disbeliever (kāfir). Only the people have need, that the Imam (as) accepts from them, Allah, the Mighty and Majestic, said: ﴾Take from their wealth some alms, with which you make them pure and purify them﴿. [Source: al-Kāfī, v 1:pg  537]

قال الإمام أبو عبد الله عليه السلام: من زعم أن الامام يحتاج إلى ما في أيدي الناس فهو كافر، إنما الناس يحتاجون أن يقبل منهم الامام، قال الله عز وجل: ﴿خذ من أموالهم صدقة تطهرهم وتزكيهم بها﴾. [المصدر: الکافي،ج ١:الصفحة ٥٣٧]