I gave my little boy a pillow from the age of 1 & he slept so much better.
I gave my kid a pillow once he started showing preference for using one when he napped on my bed, around 13 months. I got a small firm toddler pillow. He's slept so much better since tbh.
They say from the age of 1. We introduced a pillow and duvet at about 13 months. But she didn't really start to use them till around 20 months, before then she'd kick the duvet off and didn't use the pillow
My little girl was just over 2 when I introduced a pillow and I only did it as I noticed she would start to put her teddy underneath her head in the cot
Pillow in her cot from 14ish months, still in sleep bags so no duvet yet. She loves her pillow!
When they are no longer in a cot.