Grading: The hadith is sahih.
Technical note / Defect ('illah): Placing hijrah before understanding of the religion (al-fiqh fi al-din) in this order is "shadh" (anomalous), because in the preserved (mahfuz) narrations, as will come, knowledge of the Sunnah and understanding of the religion are placed before hijrah.
Important point: The author's (al-Hakim's) chain is "hasan" because of Yahya bin Uthman bin Salih; he has some softness (weakness), but he has been corroborated.

Reference / Source: Al-Daraqutni (1086) and al-Bayhaqi (2/119) narrated it via the trustworthy narrator Abu al-Zinba' Rawh bin al-Faraj from Yahya bin Bukayr with this same chain.

Reference / Source: Al-Tabarani narrated it in 'al-Mu'jam al-Kabir' (17/606) via Abd Allah bin Salih, the scribe of al-Layth, from al-Layth bin Sa'd.

Corroborating chains and supporting reports: Al-Fudayl bin Iyad, with al-Nasa'i (857), corroborated Jarir in this same order from al-A'mash, but with him the wording is "the most knowledgeable of them in the Sunnah" instead of "the most learned of them in understanding".

Technical note / Defect ('illah): A number of trustworthy students of al-A'mash, among them Sufyan bin Uyaynah and Abu Mu'awiyah al-Darir, contradicted Jarir and al-Fudayl and narrated it from al-A'mash with this same chain placing knowledge of the Sunnah before hijrah; this is how Ahmad transmitted it in 28/(17097) and 37/(22340), as did Muslim (673), al-Tirmidhi (235) and Ibn Hibban (2127) and (2133). In one narration with Muslim, instead of "sinnan" (age) the word is "silman" (i.e. Islam, precedence in accepting Islam), and this is an anomalous (shadh) narration.
Note / Clarification: In the narration of Muslim and others there is also the addition: "A man should not lead another man in prayer within his authority, nor sit in his house on his takrimah except with his permission."
Important point: "Takrimah" means the bedding, carpet or the like that is spread out for the master of the house and reserved for him.
Reference / Source: Ahmad transmitted it in 28/(17063), (17092) and (17099), as did Muslim (673) (291), Abu Dawud (582), al-Nasa'i (980) and Ibn Hibban (2144), via Shu'bah from Isma'il bin Raja', but he dropped knowledge of the Sunnah from it.