He's a deeply distressed person keen to retire (10)
I believe the answer is:
sleepyhead
'he's a deeply distressed person keen to retire' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'he's a deeply distressed' is the wordplay.
'distressed' indicates anagramming the letters.
'hes'+'a'+'deeply'='hesadeeply'
'hesadeeply' is an anagram of 'SLEEPYHEAD'.
Can you help me to learn more?
(Other definitions for sleepyhead that I've seen before include "Lazy or tired person" , "Yawning child?" , "Lazy or inattentive person" , "Person given to napping" , "dozy kid?" .)