If his coaches have looked at him and decided his ready to turn pro then they will know best.
There's been quite a few quality fighters turn pro before the age of 18. Over here there's the likes of Ryan Scope, Jordan Desbourough and Paddy Pimblett who turned pro young and did/are doing well.
Off the top of my head i'm sure Jordan Mein and Rory MacDonald turned pro when they were 16. Actually i think MacDonald had not long turned 16.
I'm not saying every 16/17 year old fighter should be looking to turn pro but there are some who are more than good enough and if they are good enough and want to fight pro and their team think they are ready then fair enough IMO.