Is a 10yo too young?

[nosoworried]

After looking for ages for a job, I have managed to find one, but that means I can not pick up my 10yo (Y6) from school. We have about 5 bus stops (10mins) to our home with about 15 mins walk to a bus stop from school. My 10yo finished 10mins earlier then my older child in Y9.
AINBU to think that it is ok for a younger child to wait for their older sibling by the school (both schools are 3 mins walk) and for them both to travel home together? Older sibling is ok with that (reluctantly, naturally!)
Dad will get home after an hour after children.
I have been SAHM (but running my own little business on the side) for as long as they were born, so, naturally, hyperventilating to let them out of my sight.
We live on the outskirts of London.

I used to let my son in year 6. He has ASD and no older sibling to go with but he managed fine. I did the run with him beforehand to show him when to press the button and made sure he double checked with the driver that he'd gotten on the right bus. I also put a family tracker app on a phone and sent it to school with him, and my work allowed me to keep on eye on it during the 10 min journey so I could make sure he defiently got on and off the bus in the right place

After your update OP I would be even more OK with this option. In reality the greatest potential danger to school children going home is traffic and yours don't cross any roads. I would just confirm what they should do in different scenarios but I expect they would work that out anyway. @Purpleraiin's advice for a phone tracker is a good call too.

Not far and lots of other children and parents walking same way so admittedly easier than the OP’s situation.

Lots of final year primary kids start doing this in prep for high school

It’s a nope from me.