Looking back in history and mythology the Fountain of Youth have always been a major myth in the human culture and can be considered an example of ancient dreams to achieve immortality by rejuvenation.
Rejuvenation has always been a desire of humanity and many alternatives were studied and proposed but with few, if any, positive results at least non scientifically proved as seriously effective.
Modern science is taking seriously such myth and several techniques to expand human lifespan has been proposed, one of them is rejuvenation, possibly on a periodical basis.
Rejuvenation is considered today as a medical discipline focused on the practical reversal of the aging process.
Rejuvenation is distinct from life extension.
Life extension strategies often study the causes of aging and try to oppose those causes in order to slow aging. Rejuvenation is the reversal of aging and thus requires a different strategy, namely repair of the damage that is associated with aging or replacement of damaged tissue with new tissue. Rejuvenation can be a means of life extension, but most life extension strategies do not involve rejuvenation.
Obviously a healthy lifestyle , food, physical exercise, specific medicines are factors that contribute to a healthier life but are not determinant on the long range.