Oldster led astray by a bit of a youngster? (5)
I believe the answer is:
elder
'oldster' is the definition.
(thesaurus)
'led astray by a bit of a youngster?' is the wordplay.
'astray' indicates an anagram.
'by' means one lot of letters go next to another.
'a bit of a youngster?' becomes 'er' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'led' is an anagram of 'eld'.
'eld'+'er'='ELDER'
Can you help me to learn more?
(Other definitions for elder that I've seen before include "could be a church leader" , "Senior - presbyter" , "Senior churchperson" , "Senior type of tree?" , "Tree and Mormon church officer" .)