To play devil's advocate, the difference between these two groups is not just their disposable income, it is their buying habits. The habits of 14-24 year olds are far less set than those of the older generations.
If you look at life time value, hooking a 14 year old on your brand (of soda, chips, shampoo, whatever) has high LTV, whereas a 45 year old will just plain buy less X.
Of course it does depend on your market. I bet the luxury car market ignores the 14-24 year olds.
Sure, back when industries weren't on an endless cycle of cost cutting and when consumers (esp. 14-24yo) actually had an attention span, LTV was something marketers could rely on. Today the younger the consumer, the more fickle which equates to no loyalty and endless churn.
If you look at life time value, hooking a 14 year old on your brand (of soda, chips, shampoo, whatever) has high LTV, whereas a 45 year old will just plain buy less X.
Of course it does depend on your market. I bet the luxury car market ignores the 14-24 year olds.