A good starting point for this is chronology.
Plato was born to an aristocratic family in Athens in 424, followed the philosopher Socrates, left Athens after Socrates death in 399, and after some years of travel returned to found his academy in approximately 384 (the approximate date of Aristotle's birth. Plato died in 348.
Aristotle was born in Stagira in 384, to a father who was a court physician to the Macedonian king Amyntas. He went to Athens in 367 (at approximately the age of 18) and stayed there studying in Plato's Academy for 20 years, only leaving in 347, after Plato's death.
Thus when Aristotle arrived at the Platonic Academy as a teenager, Plato was already a middle-aged philosopher who was at the height of a fairly distinguished career. Although he seems to have recognized that Aristotle was a promising student, Aristotle was just embarking on his career at Plato's death.
Moreover, at the end of his life, Plato was focussing on metaphysics (the idea-mathematicals) and Aristotle would have been involved in areas of practical reasoning which were a bit outside the main areas of focus of the Academy of the period.