As much as I'm a big supporter of law enforcement, if an officer told your mom that it is "illegal" for a 16-year-old to ride 90 miles solo I believe he is full of it (personal opinion as I am not a legal expert). 16-year-olds can drive coast to coast, take a train or bus cross country, or even take international flights without a guardian present. If mom said "no" she could have him picked up as a runaway but unless there is some whacked law where you live, a 90-mile cycle ride with parental consent should be no different than a 90-mile car trip. Maturity varies wildly among 16-year-olds (the same could be said for 40-year-olds) so it would really be up to the parent to decide if their teen is ready to handle such a venture.