As other reviewers note, Age 13 seems rigid, clunky and stiffly acted from a 21st-century perspective. However, it may have had wide distribution and a very important and positive impact for viewers at the time.
For me, it was interesting to try and imagine some of the other things that might have been in the minds of people while seeing this kind of material in the mid-1950s. The Korean war? Reconstructing Germany? The music of Stockhausen, Pierre Boulez, Little Richard, Duke Ellington or Jackie Wilson? Only someone old enough to remember can really know. Also interesting for me is how Age 13 portrays the institutional approach to child psychoanalysis and psychotherapy at the time. How much things had changed, even twenty years later.
The fantastical runaway sequence, starting at 21 minutes, was reminiscent of the final scene of Francois Truffaut's 400 Blows ('Les 400 Coups') of 1959, in which the troubled young protagonist also flees his environment - but ending with sadness and ambiguity rather than the convenient settling down and happy ending that is cosily portrayed here.