Princess has aged no end (6)
I believe the answer is:
isolde
'princess' is the definition.
(I've seen this before)
'has aged no end' is the wordplay.
'has' becomes 'is' (I can't justify this - if you can you should give a lot more credence to this answer).
'aged' becomes 'older' (synonyms).
'no end' means to remove the last letter.
'older' with its last letter removed is 'olde'.
'is'+'olde'='ISOLDE'
Can you help me to learn more?
(Other definitions for isolde that I've seen before include "Wagnerian heroine" , "Arthurian queen" , "for Tristram" , "Lover of Tristan" , "Irish princess" .)