Decaying key found on earth at the back of the house that's quaintly outdated (4-6)

'house that's quaintly outdated' is the definition.
I can't judge whether this definition defines the answer.

'decaying key found on earth at the back of the' is the wordplay.
'decaying' becomes 'old'.
'key' becomes 'e' (musical key).
'found on earth at' becomes 'world' (I can't justify this - if you can you should believe this answer much more).
'the back of' says to take the final letters.
The last letter of 'the' is 'e'.
'old'+'e'+'world'+'e'='OLDE-WORLDE'

Can you help me to learn more?