Not only does it vary by breed, but it varies quite a bit within the breed, and also varies depending on what time of year (or amount of available light) when the pullet is reaching the age when she could start laying.
It can also be affected by diet. Case in point: 2 years in a row, I started chicks from the same source as a friend. One year, we both got them the same day from the same feed store. The following year, I provided him, and an other friend with some of my incubated chicks. Both years, my chicks were put on fermented feed, while his were fed the standard fare. All other aspects of husbandry were very similar. We live in a small community, so both friends purchase their feed from the same 2 stores. Both years, my chicks started laying about 2 weeks before the chicks of either of my friends.
It can also be affected by diet. Case in point: 2 years in a row, I started chicks from the same source as a friend. One year, we both got them the same day from the same feed store. The following year, I provided him, and an other friend with some of my incubated chicks. Both years, my chicks were put on fermented feed, while his were fed the standard fare. All other aspects of husbandry were very similar. We live in a small community, so both friends purchase their feed from the same 2 stores. Both years, my chicks started laying about 2 weeks before the chicks of either of my friends.