When we first meet the original Turaga (Vakama, Nokama, etc), they have lived on Mata Nui for over 1,000 years, and have built their civilization effectively from scratch there while under constant attack from Rahi controlled by Makuta Teridax. As such, I always assumed their general wisdom, apparent physical frailty, and role as village elders were the natural results of their great age and accumulated experience and knowledge. This seems to be supported by the fact that they were the only inhabitants of the island (besides the Makuta) who were aware of the wider universe beyond Mata Nui for over a thousand years.*
But in the second movie, we see Toa Lhikan transform from a Toa into a Turaga and immediately assume the role of a wise guide for the Toa Metru. Admittedly, Lhikan was presumably thousands of years old by the time of the events in the film. But the change in his personality is dramatic. At the beginning of the film, he seems to be a stereotypical Toa of fire; he is fiercely protective of Vakama, quick to anger against Nidhiki, and somewhat blunt and gruff towards the other Matoran while distributing Toa Stones ("Don't archive/break it!")
But the next time we see him, in the prison in Po-Metru, he uses his staff like a cane to walk and speaks and acts with a serene calm even when his own life and the fate of his entire world are at stake. He also continuously spouts such pseudo-profound wisdoms as:
"Do not rely on your memory. Look beyond your history, and see what is."
This is at the very most mere weeks after his transformation into a Turaga, which presumably occurred when the Matoran placed his Toa Stones into the Toa Suva in the Great Temple.
So, is the apparent great age and wisdom of the Turaga actually the result of their long life? Or does the transformation immediately change their personality and outlook to satisfy the requirements of the role of an elder adviser?
Considering that it was eventually revealed that
the Matoran, Toa, Turaga, and Makuta were all created by the Great Beings to maintain the operations of the enormous space robot known as Mata Nui, whose body they inhabit,
it seems reasonable that their biomechanics could be "prefabricated" for this role. But I'd like to know if there's any more evidence I've overlooked.
*With the exceptions of Akhmou, who was lied to by Makuta, and Matoro, who learned while serving as translator for Turaga Nuju.