When did Shakyamuni became buddha? We know Shakyamuni was a prince and had all the lavish life a prince should have. He was isolated from every pain and suffering as we are told. As he traveled countryside he began to feel pain and suffering in others and witnessed death. He could have been ignorant or at most have donated some of his wealth to the commoners, but he didn't. He left the life he had, and set out to seek the ultimate truth of life. At Gaya, he meditated and got enlightened and became a buddha as most of us are told.

OK, above mentioned is what we all know. Problem is, what if he had not decided to leave the prince-hood? What if he didn't have that curiosity? Isn't the first step he took by leaving his old life behind, a sign of becoming buddha? I believe that step as the sprout of enlightenment.

Please, explain if I am wrong.
[unconfirmed, proceed with caution] since in his previous lives he already was a bodhisatta and so a noble disciple, becoming awakened was only a matter of time since according to the Dhamma after attainment of the sotapatti noble level (the 1st of the four) nibbana is to be attained within 7 lives at the most.

thus the Buddha was predestined to become one. even he himself couldn't change that. it's only that all his previous practice and wholesome kamma ripened in that particular life 2500 years ago



until the awakening he was not a buddha, but an unawakened bodhisatta


  before my Awakening, when I was an unawakened bodhisatta


Ariyapariyesana sutta (MN 26) by Ven Thanissaro Bhikkhu