We say something 'exemplifies' something else, when it:
a. represents the something; and
b. is the something (or, more correctly: it possesses the qualities of the something).
Here, Nikos is exemplifying boyhood.
(He and I made the pistol with an old bedrail, jigsawed and painted black. I fixed the 1950s holster with my belt and some tacks. Ruth supplied the hat.