My lad did CBT at 16 but only rode his 'ped for a few monhts as all his mates had cars, passed his car test just before his 18th birthday last year, it's pretty hard to justify a bike on economy grounds against a small car unless you run a 125 or similar and no where near as convenient or safe.
He's just coming up 19 and talking about maybe doing his bike test, part of me would love him to experience the freedom of two wheels but a big part of me is nervous of the safety implications.