When younger ones attain Paramapadam, the elders do not accept the pitru sesham. Why differentiate the souls in terms of young or old? I have asked this question put forth to me.

Yes, when younger ones attain Paramapadam, the elders do not accept the pitru sesham though all of us are souls. But a relationship cannot be altered, a father is a father, and a son is a son. Hence this practice, moreover there is no need for the elderly to accept the sesham.