Each year, more and more houses are built further and further away from city cores and reliable transit services. While many developments are intentionally planned for walkability to a "town center", many homes are built out of this range. Then consider this: how many car-enabled residents would value the two-minute drive over the twelve-minute walk? Then consider the implications for the non-car enabled- say, younger teens. Are we sure that all of these pre-adults want to "endure" the round-trip walk? (Take Mom's taxi service out of the picture for now). Simple solution- bicycles. As I believe, most American kids have one in their garage. Bicycle infrastructure- either a wide shoulder for the road or a wider sidewalk, and bike racks in good repair- would enhance this transportation mode's appeal for all, and increase younger teens' sense of mobility.
In the meanwhile, as developed areas have continued to sprawl, States have been raising minimum driving ages, although the trend has cooled off in the past year. (Thankfully, the Allstate-insurance sponsored National STANDUP Act failed after the last election). What this has likely led to (I should find evidence or uncover it myself) is that teens are probably spending more time at home. Furthermore, another issue with higher driving ages is reduced employment opportunities because of lack of transportation. I suspect that the decrease in teen (ages 16-19) summer employment is at least in part directly linked to this issue. (Mama and Papa have been your chauffeur for so many years now...).
Working close to home has its perks, but America has a mobile workforce, teens traditionally included. If the teen is lucky, he or she will find a job within their means of commuting- by foot or bike. So how do we extend the mobility range of pre-licensed teens? Give them powered wheels. Easy-to-use and maintain powered scooters and mopeds are practical options that can give "reliable transportation" to more teens, thereby increasing their competitiveness in the entry-level job market. Such scooters are common in Europe, although less so in America.
Part of this is a culture thing- in days past, before 17 yo driving ages and passenger limits- teens in high school probably had little problem finding a ride, so there wasn't too big of a suburban teen market. The next thing is that a number of states require license plates on select classes of scooters and licenses for operators. However, in many states, golf carts, even when driven on a public street, are exempted from these vehicle and operator licensing requirements- and are ubiquitous in a number of communities. So perhaps we could see more of these vehicles around in the future.
Note that I did not list socioeconomic implications on the diffusion of teens in the workplace: many licensed teens don't have access to cars due to economic factors. The effect of this can be quite pronounced; at a park where a car is a virtual necessity to access, the high-school aged waterfront lifeguards were clearly a standard-deviation-plus above socioeconomic norm even for the tony County the park was in.