I know that cot bumpers shouldn’t be used during the first 12 months of baby’s life, but how about after that?

Red Nose has the following information about the use of bumpers in a cot.
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