quintilian on the excesses of young artists ("boys")... (of course, in the rubric of classical rhetoric)

Now there are three forms of narrative, without counting the type used in
actual legal cases. First there is the fictitious narrative as we get it in
tragedies and poems, which is not merely not true but has little resemblance
to truth. Secondly, there is the realistic narrative as presented by
comedies, which, though not true, has yet a certain verisimilitude. Thirdly
there is the historical narrative, which is an exposition of actual fact.
Poetic narratives are the property of the teacher of literature. The
rhetorician therefore should begin with the historical narrative, whose
force is in proportion to its truth. I will, however, postpone my
demonstration of what I regard as the best method of narration till I come
to deal with narration as required in the courts. In the meantime, it will
be sufficient to urge that it should be neither dry nor jejune (for why
spend so much labour over our studies if a bald and naked statement of fact
is regarded as sufficiently expressive?); nor on the other hand must it be
tortuous or revel in elaborate descriptions, such as those in which so many
are led to indulge by a misguided imitation of poetic licence. Both these
extremes are faults; but that which springs from poverty of wit is worse
than that which is due to imaginative excess. For we cannot demand or expect
a perfect style from boys. But there is greater promise in a certain
luxuriance of mind, in ambitious effort and an ardour that leads at times to
ideas bordering on the extravagant. I have no objection to a little
exuberance in the young learner. Nay, I would urge teachers too like nurses
to be careful to provide softer food for still undeveloped minds and to
suffer them to take their fill of the milk of the more attractive studies.
For the time being the body may be somewhat plump, but maturer years will
reduce it to a sparer habit. Such plumpness gives hope of strength; a child
fully formed in every limb is likely to grow up a puny weakling. The young
should be more daring and inventive and should rejoice in their inventions,
even though correctness and severity are still to be acquired. Exuberance is
easily remedied, but barrenness is incurable, be your efforts what they may.
To my mind the boy who gives least promise is one in whom the critical
faculty develops in advance of the imagination. I like to see the first
fruits of the mind copious to excess and almost extravagant in their
profusion. The years as they pass will skim off much of the froth, reason
will file away many excrescences, and something too will be removed by what
I may perhaps call the wear and tear of life, so long as there is sufficient
material to admit of cutting and chiselling away. And there will be
sufficient, if only we do not draw the plate too thin to begin with, so that
it runs the risk of being broken if the graver cut too deep. Those of my
readers who know their Cicero will not be surprised that I take this view:
for does he not say "I would have the youthful mind run riot in the
luxuriance of its growth?"

Quintilian, Institutio Oratorio

…but where is the threshold past which there is no mercy?