Being wise, saints conceal their age! (5)
I believe the answer is:
sages
'conceal their age' is the definition.
I can't judge whether this defines the answer.
'being wise saints' is the wordplay.
'being wise' becomes 'sage' (similar in meaning).
'saints' becomes 's' (this could be a standard abbreviation of which I'm unaware).
'sage'+'s'='SAGES'
Can you help me to learn more?
(Other definitions for sages that I've seen before include "Wise people" , "plants" , "Learned people" , "enlightened people" , "Pundits" .)