Inclined as old boy to spill secrets while talking (7)
I believe the answer is:
oblique
'inclined' is the definition.
(similar in meaning)
I can't explain the remainder of the clue.
(Other definitions for oblique that I've seen before include "Slanted" , "This angle is obtuse or acute" , "Indirect - evasive" , "Aslant" , "slash" .)