How old was your baby when did you do this?

Hi there i have a 10 month old baby, i was just wondering at what age did you start using their cot quilt? it says on it from 1year old, but i was thinking about starting it now because its getting so cold we do put her in a 'growbag' but she doesn't like them and is staring to outgrow them and i don't fancy buying more because it will start warming up soon, and she doesn't seem to keep still at night lol she starts at one end and ends up somewhere else, why is it not suitable for a baby under 1? is it ok or not? any advice would be great :)