If I had a 16yo kid, only cars I'd let him/her have/drive would be a new 997S Coupe/S-Class.....my logic being that, in hands of a responsible driver, those are two of world's safest cars (when considering both active and passive safety). And if I haven't imbued responsibility in a kid by age 16, I prob have failed as a parent anyway.....
An irresponsible driver will find a way to kill/injure himself in any 150hp car you give him anyway....and any SUV (esp poor emgcy handling/rollover risk/roof strength issues)/econobox/older car (primitive air bags, stab ctrls, etc) is unlikely to be as safe as 997S/S-Class in both avoiding an accid and protecting your kid if the unavoidable happens (let's also consider that responsible teenage drivers can be hit by an inattentive middle-aged/elderly driver)....
Re: the motivation argument, I'd argue it's case-specific...sure, trust fund kids tend to have motivation issues, but Bill Gates and many guys in financial business were originally trust fund kids themselves......know lots of guys in the tech and financial businesses in their 30s who are worth >$100MM from their own career earnings.....most have been workaholics all their life, even after they've made their money....they simply enjoy their work, and they also enjoy their toys responsibly.....would argue those who display maturity and high achievement in their education and career tend to be better balanced in their risk/reward decision-making re: driving as well.....