Is it permissible for a non-mature person to deliver the khutbah, whilst another person leads people in Salah?
For a person other than the Khateeb (deliverer of sermon) to lead the salah is against the preferred ruling. For a non-mature to deliver a khutbah is a issue which is differed upon. Some say it is impermissible and thus the obligation shall not be fulfilled whilst other scholars state its permissibility. Thus, it is inappropriate or doubtful for such a person to deliver the khutbah and should be avoided.
And Allah ﷻ knows the best
Imam Ahmad Rida Khan رحمة الله تعالى عليه
Translation by Dr Musharraf Hussain Al-Azhari Translator of Majestic Quran, www.majesticquran.co.uk