At 15 I started to bike everywhere. I took my bike to the Hudson river path and I could get anywhere I wanted in 10-20 minutes - visiting a friend who lived downtown, or head up to Central Park to meet up and bike around with others, try out some diners uptown, etc.
At 16 my friends and I would walk around the east side, walking for miles in the middle of the night.
I don't think it was negligent at all, but I felt extremely independent because I could get anywhere as a kid without needing a car. I've always found that growing up in a city that felt safe and had great public transportation made me extremely independent at an early age.