Old enough to master true form? (6)
I believe the answer is:
mature
'old' is the definition.
(associated in meaning)
'master true form?' is the wordplay.
'master' becomes 'ma'.
'form?' indicates anagramming the letters (I've seen 'form of' mean this).
'true' with letters rearranged gives 'ture'.
'ma'+'ture'='MATURE'
'enough to' is the link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for mature that I've seen before include "Ripe or fully grown" , "sensible" , "Fully developed physically" , "Fully grown and adult" , "of older years" .)