What does the cryptic crossword clue "Chirpy types heading off youthful disease (7)" mean?

The definition is "disease". The wordplay uses a deletion. RICKETS (deletion) = RICKETS; definition: "disease" The answer is RICKETS.

Chirpy types heading off youthful disease (7)

Guardian Cryptic #29423 | 8 Down | 2024-07-01 flower