Sometimes you act like one … 
if you’re good enough you’re old enough its that simple, most of the experienced alleged “drivers” where I work I wouldn’t trust to sweep the yard.
Retired now,when I was working I had nothing against young Drivers in a general sense,
It was the few youngsters that I did come across that thought they where the bees knees because they could now drive class 1,coming into the yard or a depot swinging around one handed at an unreasonable speed,in a word “exhibitionist” and if you said anything their lips started flapping.
Those type are the one`s that get noticed and get decent youngsters tarred with the same brush.
My lad took his rigid test a few months ago
He’s 19
Now he’s down London most days in a 26 tonne rear steer big space mercedes
He goes to the likes of downing street and parliament
He never seems phased by his days work
As long as he stays safe
I’m very proud of him
I was on artics at 21, I’ve never looked my age and was often asked if I ‘was old enough to drive that big thing son’…in fact I still am 
…, ok, I’m lying about the last bit 
I passed my class1 test at 10am…back into the yard,lifted 3 log books,then went and loaded timber for 5 drops south coast.big j4…180 gardner,5 speed,no power steering,no alternator,just 4 batteries in the passenger pit to last the week,and better mirror on a budgies cage.never had driven anywhere outside of Glasgow beforehand.got a dude to show me that funny twisty dolly knot thing that drivers used to be able to do to stop all the stuff falling off. flat to the mat,and never looked back.just winged it all the way.never wrecked anything other than the odd mirror or lens.used to get stopped regular on the 74/75 looking for my dad or whover was meant to be driving as at 21, I looked 16… if you can drive,then drive…its the insurance that bolloxes it all up.
I also started at co op when I was 20, jumped straight in on class 1. Good thing there is you learn to reverse them pretty quick with all the dodgy deliveries we do 