Died in his forties, but in some ways he was 56 (5)
I believe the answer is:
elvis
'died in his forties but in some ways he' is the definition.
The definition suggests a singular noun which matches the answer.
'56' is the wordplay.
I cannot quite understand how this works, but
'56' could be 'lvi' (Roman numerals) and 'lvi' is present in the answer.
The remaining letters 'es' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
'was' acts as a link.
Can you help me to learn more?
(Other definitions for elvis that I've seen before include "'The King' (singer)" , "Much-impersonated singer, d. 1977" , "Legendary singer" , "Mister Presley for one" , "Singer Presley" .)