My (just) turned 4yo is still rear facing. She's not asked to turn around, despite having an older sibling who is forward facing.
She is very small for her age (1st centile) and will probably 'fit in terms of weight and height for several years (probably 7-8!). She's got some medical issues/had major neurosurgery, which means I'm a bit paranoid about significant bangs to her head.
I'd assumed I'd turn her at 4, but she's comfortable and happy and fits fine. She's ngoing to school this year, of that's a factor in terms of embarrassment.
Is it a practicality thing turning them at 4 or are there continued safely advantages to waiting? If she's happy and it's safer, then I guess why turn her. But equally, because of heath (and being tiny) she's babied quite a lot for her age?