It is obligatory on the individual to refer to the marja in learning about the religious rulings and implementing them in the matters of his worships, dealings, family relations and relations with other people, since the sharia has rulings and guidance for all issues that one could run into.
In other aspects of life, the marja is referred to as an advisor since he has knowledge on the Holy Quran and the teachings of the Ahlulbait (peace be upon them).

Religious adulthood is recognized for the male by any of the following three signs, whichever happen first:
1. The presence of hard hair on his face or in the pubic area.
2. The release of semen, whether it was during a wet dream or when awake.
3. The completion of fifteen lunar years.
The female reaches adulthood when she completes the age of nine lunar years.

Taqleed is an obligation based on intellect. Muslims are required to implement the laws of the Islamic religion, and they cannot be known in details and in a correct way except by referring to the people of expertise, who are the religious scholars and relying on them in their findings that they concluded by research and study.
Evidence of this concept from the Holy Quran is when Almighty Allah said: “And the believers should not all go out to fight. Of every troop of them, a party only should go forth, that they (who are left behind) may gain sound knowledge in religion, and that they may warn their folk when they return to them, so that they may beware.”(Qur'an, 122:9).

Your previous Taqleed is valid and you can continue to follow his Eminence.

Emulation (taqlīd) is a necessity when a lay believer faces a situation where he does not know the correct religious ruling, as he is supposed to refer to the expert to get the proper answer. Otherwise, without referring to the expert and implementing the ruling, he would be liable for the mistake, whereas he will not be liable when he refers to the expert, even if the latter made a mistake. Taqlīd secures a layperson from liability before the Almighty Allah.

The popularity of the concept of (taqleed) amongst the masses in these days is due to the broad existence of means of communication which have led to the wide spread of knowledge of religious laws. It is not because the concept is new. Rather, it was present at the time of the Imams (peace be upon them) when they were directing their companions and followers, in general, to learn the religious laws. This naturally led to many people asking questions about their affairs, and it was not practical for all of them to reach the Imam (peace be upon him) and ask him in person, so they used to refer to his close companions who could be reached to gain knowledge in religious laws. There were known narrators who were giving edicts to people and the Shias used to refer to them during those days, like Muhammad bin Muslim, Zurarah, Zakariyya bin Adam and others.
This need continued to exist after the occultation of the Twelfth Imam (peace be upon him) until now.
It is a natural need and a sensible process, as people refer to the experts in various fields like medicine, engineering and other kinds of expertise, as people are not satisfied with their own limited knowledge in these areas.

One will begin doing the taqleed, by referring to and acting upon the edicts of the religious scholar who has reached the level of ijtihad, has the qualifications of a marja and he is the most knowledgeable.

If the edicts of the Marjas are different in any particular issue, one must follow the most knowledgeable. If his opinion is an obligatory precaution, one has a choice of following him by acting upon the precaution or referring to another Marja provided that the latter is more knowledge than the rest of the Marjas.

It is permissible to act in precaution by ensuring that one’s acts are not against the edicts of any one Marja. This will not be considered to be emulation (taqleed).