Zaid Alsalami, Shaykh Dr Zaid Alsalami is an Iraqi born scholar, raised in Australia. He obtained a BA from Al-Mustafa University, Qom, and an MA from the Islamic College in London. He also obtained a PhD from... Answered 1 year ago

Bismihi ta'ala 

There is no specific significance to the number 18 in Islam, and it is not connected to maturity in Islam, from what we can see from our mainstream Islamic tradition.

And Allah knows best.