What is the definition of 'Kahil' (mature/adult age)?

Primary text

'Kahil' refers to those who have passed the age of thirty. This definition is supported by the interpretation of the verse in Surah Al Imran (Quran 3:46) regarding speaking in the cradle and as a 'Kahil'. The term is derived from the description of vegetation that has become complete and strong ('Ikhtalaha al-Nabatu). A person remains in the stage of 'Kahil' until reaching fifty, after which they become elderly ('Shaykh') until death.