Age? 2 years, 9 months.
It's wild.
I grew up at a time and a place where I had a lot of independence. I rode a bike everywhere. I'd do things by myself and with friends. I actually feel sad for kids nowadays. Being a kid now seems to be being at home or getting shuttled from preplanned activity to preplanned activity in a car.
Almost everywhere in the US, it's really not possible to do it any other way because the entire infrastructure is predicated on car ownership.
Fears of abduction and worse are real of course but the risks are overstated. I actually think these risks are made worse by the ubiquity of cars. I mean think about it: it becomes a lot more difficult to abduct someone without a private vehicle.