The average is that a bird will start laying around 6 months and will lay well for about 3 years (they may keep laying here and there as they age but not consistently). But, these are just averages and there are lots of factors.
Commercial birds like Leghorns lay very well and will lay an egg a day, sometimes 2. They start younger, lay the most consistently, but are spent faster. Heritage birds tend to start laying a little later and might not lay quite as well as a commercial birds (ie not every single day) but will then continue laying a little longer.
Other factors that effect laying are whether or not you encourage your birds to lay through the winter, diet, broodiness, etc.