Its a touchy subject. I think the age is a bit of a deterent when it comes to making tough decisions. Sure the 1500+ hour CFI will have a better grasp on making good pilot decisions but I'd certainly feel much better if the guy up front wasn't still dripping behind the ears. Say what you will about hours and experience but LIFE itself gives you just as much real world knowledge and experience.
I know at 20, 21, 22 years old I was nowhere NEAR ready to sit up front in a transport category aircraft.