Neil wrote:

> (a) m ar n-olus aidh fin
> (b) fios na n-g s na naos

>> (a) Greater than our knowledge by itself
>> (b) (is) the knowledge of the young and the old
>>     [is the knowledge of precedent and tradition]

> However, if we have here a substantivised adjective corresponding to
> 'g' (young person), wouldn't it be 'esach' or 'esta' ('old person'),
> rather than 'es'? (I note that FGB lists [under g]: 'idir g agus
> aosta'.)

True, but I can imagine the poet truncating "esta" metri gratia.

> 'es' itself is a noun which means 'age' rather than 'aged person'. As
> such, wouldn't 'es' be contrasted with 'otiu' (youthfulness), rather
> than 'g' (young person)? (Cf. DIL A 80.33: etir es & etid).

I think these are valid reservations.  Luckily we have your
reading of "knowledge/learning of precedents and traditions"
to hang our hat on.  The "g" and "es" as youth and age might
still stand as resonant word-play.