The gotra is sometimes optionally regarded as yuvan when respectful reference to him is intended.,
The word Vriddha is another term for Gotra. As तत्र भवान् गर्ग्यायणः or गार्ग्यः \you honored Gargyayana or Gargya\. This sutra is in fact a Vartika and not a sutra of Panini. Similarly तत्र भवान् वात्स्यायनः or वात्स्यः, तत्र भवान् दाक्षायणः or दाक्षिः ॥
Why do we say 'when respectful reference is intended'? Observe, वात्स्यः and गार्ग्यः ॥ The definition of Vriddham as given by other Grammarians is अपत्यमन्तर्हित वृद्धम् ॥,