What does the cryptic crossword clue "Youth doesn't start growing a lot (8)" mean?

The definition is "growing a lot". The wordplay uses a deletion. TRIPLING (deletion) = TRIPLING; definition: "growing a lot" The answer is TRIPLING.

Youth doesn't start growing a lot (8)

Guardian Cryptic #29097 | 21 Across | 2023-06-15 flower