"I thought: 'Not only does Alara Kalama have conviction, persistence,
mindfulness, concentration, & discernment. I, too, have conviction,
persistence, mindfulness, concentration, & discernment. What if I were
to endeavor to realize for myself the Dhamma that Alara Kalama
declares he has entered & dwells in, having realized it for himself
through direct knowledge.' So it was not long before I quickly entered
& dwelled in that Dhamma, having realized it for myself through direct
Alara Kalama was the Buddha-To-Be's first ascetic teacher, and he taught the sphere of nothingness, the 7the Jhana. I'm not sure his learning of this absorption has a date, but the Buddha was an ascetic for about six years, and must have already mastered the earlier concentrations.
There is no sign of him struggling with it, and this sutta is more about his difficulty in giving up the pursuit of wealth and a happy family live -- upon learning of sickness, old age, and death.