This is a portion from the Hadīth al-Jibraīl – in which Jibraīl عليه السلام asks the Prophet ﷺ a few questions which the Prophet ﷺ responds to.
The understandable transalation of this portion is: “he (Jibraīl عليه السلام) came in such a form that he had extremely black hair.”
At this point my teacher explained that although knowledge is to be sought from the cradle to the grave, one should strive to seek it most during their youth as during that period one is free from many responsibilities and has the strength to put behind it – one is able to travel to, whereas at an old age it maybe difficult.