Developed pleasure in penning two lines and good further line (4-5)
I believe the answer is:
'developed' is the definition.
'good further line' is the wordplay.
'good' becomes 'full' (synonyms).
'further line' becomes 'grown' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'pleasure in penning two lines and' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Another definition for full-grown that I've seen is "Adult".)