SB 11.28.41
kecid deham imam dhirah
su-kalpam vayasi sthiram
vidhaya vividhopayair
atha yuñjanti siddhaye
Translation:
By various methods, some yogis free the body from disease and old age and keep it perpetually youthful. Thus they engage in yoga for the purpose of achieving material mystic perfections.
Purport:
The process described here is meant to fulfill one’s material desires, not to bring one transcendental knowledge. Therefore this process cannot be accepted as devotional service to the Lord, according to Srila Bhaktisiddhanta Sarasvati Thakura. Despite all such mystic perfections, the material body will ultimately die. Actual eternal youth and happiness are available only on the spiritual platform of Krsna consciousness.