Explaining that Romulus and Remus decided not to fight but to submit the decision as to how the city should be named to the Gods.
Quoniam gemini erant nec aetatis discrimen inter eos fieri [discrimen facere = discernere] poterat, necesse fuit deos consulere.
Because they were twins and (at that time? - aetatis?) discord could not arise between them it was necessary to consult the Gods.
I'm perplexed by aetatis - does it simply mean 'at that time? - or at their age, i.e. that they were so young?