Suggested highlights (see the "How to Outline a Passage" video for more info on highlighting):

P1 — Picasso could tap this reservoir of youthful experimentation
P2 — These pictures lacked childlikeness
P3 — unusually skilled rather than frankly precocious but that no word short of prodigy can describe him in his spectacular progress
P4 — As a prodigy, Picasso epitomized the second type, but, said Apollinaire, he was able to convert himself into the first.
P5 — The Portrait of Gertrude Stein (1906) stands out as an indicator of this transformation:

(Please also note: it's not important that your highlighting matches mine exactly! There may be multiple good things to highlight in one paragraph. Your goal should be to mostly highlight similar points to the ones I show here even if they're not the exact same ones.)