Herb in India, ageless until the end (8)
I believe the answer is:
amaranth
'herb' is the definition.
(amaranth is a kind of herb)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for amaranth that I've seen before include "tropical plant" , "Type of cereal" , "Never-fading flower; food colour dye" , "South American cereal; purple colour" , "Plant; purple colour" .)