The government Healthline recommends babies not have a pillow until at least 1 /12 years old and the red nose site says 2 years old. Is there an age were you know they are completely (98%) in the clear and safe to use a pillow?

Red Nose recommends that you withhold pillows (& other soft bedding) until a child is in a bed, &/or 2 years of age.
Red Nose has the following information

Soft bedding may cover the baby’s face and obstruct breathing and/or cause overheating.
Older babies in a cot can be at an increased risk of a sleeping accident by using pillows and bumpers as a step to climb up and fall out of the cot.
It is safer to wait until the child starts to sleep in a bed before introducing a pillow or other soft bedding.
https://rednose.org.au/article/at-what-age-can-i-introduce-cot-bumpers-and-pillows

Pillows are not necessary for baby and increase baby’s risk of sudden unexpected death in infancy including SIDS and fatal sleep accidents
Red Nose recommends delaying offering a pillow until baby is over two years of age and is no longer sleeping in a cot or portable cot
https://rednose.org.au/article/pillow-use