Your post gets a 'like' although I disagree with your views on segregation. The point about the 10-year-old is a very good one. There are novices of all ages on all roads and many other road users seem to expect them all to be experts ands to know how to deal with traffic.
Although I'm not too sure how many unaccompanied 10-year-olsds there are... Mine were riding accompanied very young and were out on A-Roads with me at seven or eight. But none of them ventured out alone (even in this tiddly market town) much under eleven. Even among keen cycling families, I know of no 10-year-olds who popped to footie by bike alone at the age of ten.
But that's not the point... Your observation about novices and youngsters is spot on in terms of a driver's need to accept that riders may fall into those categories.
There aren't as many as there should be, is my view.
Going back 30 years, my ex-husband tells me that at our sons age (10y) he went everywhere by bike, independantly, his parents were very happy for him to go out on his bike in the morning and return home at teatime. This is as it should be.
This is not a risk I'm prepared to take with my son. He has magnificent bike handling skills, thanks to his cycle speedway training, but I don't consider it safe for him to ride alone on our roads. Whats changed in this time? Traffic. Both the volume and speed. And sadly the attitude that anyone who ventures onto our roads if they're not inside a car can be considered collateral damage.
Sadly, the culture for driving fast, inconsiderately without care for others has gone too far.Planning roads for cars/buses/lorries has gone too far. We're not going to change this overnight.
I'd much prefer to cycle on roads where drivers respect me and my safety , drive courteously around me. But it's not going to happen. I see high quality, segregated infrastructure the only safe option, if we're to get back to a culture where the vast majority can safely hop on to a bike and ride confidently.
We don't expect people to walk in the road with cars, buses, HGV's etc and think it safe.Rightly, segregated infrastructure for pedestrians is provided. Why do we expect people to cycle there? They're equally as vulnerable as if they were on foot.