In my neck of the woods, the normal practice when boarding local city buses is that the driver will wait until you're in a seat before pulling away when it's an elderly person (potentially unsteady on their feet), a parent with youngsters etc.
If it's only younger, more able-bodied passengers who have boarded, they may wait, or might pull away before everyone is seated, on the assumption they're quite capable of looking after themselves.
I do have a diminishing supply of grey hair, but I've always thought myself a quite sprightly geezer, and have been used to the bus drivers mostly starting off before I get into my seat.
In recent months, however, I've noticed the drivers all seem to wait for me to get to my seat and 'properly settled' before they pull away. I wonder what subtle change there's been?