Complaint of youth in spring month (6)
I believe the answer is:
malady
'complaint' is the definition.
(malady is a kind of health problem)
'youth in spring month' is the wordplay.
'youth' becomes 'lad' (lad means a young man).
'in' is an insertion indicator.
'spring month' becomes 'May' (May is part of the spring).
'lad' going into 'may' is 'MALADY'.
'of' is the link.
(Other definitions for malady that I've seen before include "Afflication" , "hay fever, perhaps" , "Ailment; illness" , "Illness or disease" , "Sickness, ailment" .)