Limiting it to “actual driving age people” would be nearly as arbitrary, as not everyone of actual driving age is a driver. People who choose not to drive, who have suspended or revoked licenses, who cannot see well enough to drive, who are temporarily or permanently impaired…why count those people but not children?
So the laws simply require passengers, not passengers with any particular qualifications. Much simpler and cleaner to define, communicate, and enforce.
Eww. “Precocious” implies that his behavior is that of an adult. The answer to your question is 100% obnoxious, unless there is a stronger term for it. Deplorable?
Why such a big doggie bed? Willie isn’t going to get any bigger. Maybe this was Mom & Dad’s plan all along!