My kids, now adults, used to tease me that I was the world's most protective mother.
But even I feel shocked at how 'nannying' the world has come and I expect many posters here are young parents.
I was walking a mile to school on my own at 7. It was alongside a busy-ish local road with a 'lollipop lady' at the end as I had to cross that road. I did it 4 times a day- morning, home for lunch and back, and home time. Sometimes my Mum would walk with me.
Now, where I live, parents are driving their kids to school, when the distance is little more than half a mile from one end of the town to the school. The kids build no resilience or road sense.
IME girls are more mature than boys at this age.
It also depends on what type of train. An intercity train where it won't stop within the hour is different to a local train stopping 4 times in an hour, with doors opening and people getting off.
The OP hasn't told us much but on balance, I feel they'd be okay if they are mature.
As PPs have said, in commuter belts, children are getting trains at that age to go to school and it's just part of normal life.