Are there any special techniques maintaining a youthful appearance? Is it possible to not age at all?
Let me take the second question first. The great masters ("masters," in the sense of complete self-mastery) have power over life, death, and everything in between — including the aging process.
If they choose not to age, or to have an appearance of youth, old age, or whatever, they can have it, if they feel God wants this of them. (Self-mastery or self-realization is our destiny also, in this or some future lifetime).
But the Great Ones know without question, as we all should realize also, that this body is just a shell, a temporary home for our souls — definitely not permanent.
That doesn’t mean we should not take good care of this "home," keeping it as clean, healthy, and attractive as possible.
But being overly concerned about one’s appearance of youth or beauty is a very harmful attachment.
"You’re only as pretty as you feel inside," is the title of an old song. I feel this idea is very true!
Beauty shines from inside. A person may have little or no physical beauty by common standards , and yet he or she is radiant with divine inner light.
Is there a technique for maintaining a youthful appearance? Yes. Take good care of your body in common sense ways.
Then take even better care of your soul through prayer, meditation, good company, and a loving, giving spirit.
Finally, stay childlike in your heart. That doesn’t mean childish or irresponsible in any way. It means to maintain a joyful sense of awe and wonder at everything around you. It means simplicity and non-attachment.